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Rummel AD, Sheehy ET, Schachner ER, Hedrick BP. Sample Size and Geometric Morphometrics Methodology Impact the Evaluation of Morphological Variation. Integr Org Biol 2024; 6:obae002. [PMID: 38313409 PMCID: PMC10833145 DOI: 10.1093/iob/obae002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 11/03/2023] [Accepted: 01/19/2024] [Indexed: 02/06/2024] Open
Abstract
Geometric morphometrics has had a profound impact on our understanding of morphological evolution. However, factors such as sample size and the views and elements selected for two-dimensional geometric morphometric (2DGM) analyses, which are often dictated by specimen availability and time rather than study design, may affect the outcomes of those analyses. Leveraging large intraspecific sample sizes (n > 70) for two bat species, Lasiurus borealis and Nycticeius humeralis, we evaluate the impact of sample size on calculations of mean shape, shape variance, and centroid size. Additionally, we assessed the concordance of multiple skull 2D views with one another and characterized morphological variation in skull shape in L. borealis and N. humeralis, as well as a closely related species, Lasiurus seminolus. Given that L. seminolus is a morphologically cryptic species with L. borealis, we assessed whether differences in skull shape and in 2DGM approach would allow species discrimination. We found that reducing sample size impacted mean shape and increased shape variance, that shape differences were not consistent across views or skull elements, and that trends shown by the views and elements were not all strongly associated with one another. Further, we found that L. borealis and L. seminolus were statistically different in shape using 2DGM in all views and elements. These results underscore the importance of selecting appropriate sample sizes, 2D views, and elements based on the hypothesis being tested. While there is likely not a generalizable sample size or 2D view that can be employed given the wide variety of research questions and systems evaluated using 2DGM, a generalizable solution to issues with 2DGM presented here is to run preliminary analyses using multiple views, elements, and sample sizes, thus ensuring robust conclusions.
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Affiliation(s)
- A D Rummel
- Department of BioSciences, Rice University, Houston, TX 77005, USA
| | - E T Sheehy
- Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA
| | - E R Schachner
- Department of Physiological Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32603, USA
| | - B P Hedrick
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
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2
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Sloan NS, Kennington WJ, Simmons LW. Divergence in the internal genital morphology of females and correlated divergence in male intromittent structures among populations of a millipede. Evolution 2023; 77:2456-2471. [PMID: 37658784 DOI: 10.1093/evolut/qpad157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2023] [Revised: 08/18/2023] [Accepted: 08/30/2023] [Indexed: 09/05/2023]
Abstract
Our understanding of genital evolution comes largely from studies of male genitalia. Females have received far less attention because of the difficulties inherent in quantifying the shapes of their internal genital structures. Here we combine advances in micro-computed tomography with a new landmark free method of quantifying three-dimensional trait shape, to document patterns of divergence in female genital shape, and the correlated divergence of male genitalia among populations of the millipede Antichiropus variabilis. We used single-nucleotide polymorphisms to estimate levels of neutral genetic divergence among seven populations of millipede. Genetic divergence was high and correlated with geographic distance. Comparing phenotypic divergence in genital shape to neutral genetic divergence, we found that genital shape for both females and males has diverged more than would be expected from random drift, consistent with a pattern of directional selection. While there was significant covariation between female and male genital shape across populations, the magnitude of divergence in genital shape between the sexes was not correlated. Our results demonstrate the utility of using three-dimensional scanning technologies to examine female genital traits and add to a small but growing number of studies showing that like male genitalia, female genitalia can be under strong directional selection.
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Affiliation(s)
- Nadia S Sloan
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, WA, Australia
| | - W Jason Kennington
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, WA, Australia
| | - Leigh W Simmons
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, WA, Australia
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3
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Hedrick BP. Dots on a screen: The past, present, and future of morphometrics in the study of nonavian dinosaurs. Anat Rec (Hoboken) 2023. [PMID: 36922704 DOI: 10.1002/ar.25183] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Revised: 10/28/2022] [Accepted: 02/12/2023] [Indexed: 03/18/2023]
Abstract
Using morphometrics to study nonavian dinosaur fossils is a practice that predates the origin of the word "dinosaur." By the 1970s, linear morphometrics had become established as a valuable tool for analyzing intra- and interspecific variation in nonavian dinosaurs. With the advent of more recent techniques such as geometric morphometrics and more advanced statistical approaches, morphometric analyses of nonavian dinosaurs have proliferated, granting unprecedented insight into many aspects of their biology and evolution. I outline the past, present, and future of morphometrics as applied to the study of nonavian dinosaurs zeroing in on five aspects of nonavian dinosaur paleobiology where morphometrics has been widely utilized to advance our knowledge: systematics, sexual dimorphism, locomotion, macroevolution, and trackways. Morphometric methods are especially susceptible to taphonomic distortion. As such, the impact of taphonomic distortion on original fossil shape is discussed as are current and future methods for quantifying and accounting for distortion with the goal of reducing the taphonomic noise to biological signal ratio. Finally, the future of morphometrics in nonavian dinosaur paleobiology is discussed as paleobiologists move into a "virtual paleobiology" framework, whereby digital renditions of fossils are captured via methods such as photogrammetry and computed tomography. These primary data form the basis for three-dimensional (3D) geometric morphometric analyses along with a slew of other forms of analyses. These 3D specimen data form part of the extended specimen and help to democratize paleobiology, unlocking the specimen from the physical museum and making the specimen available to researchers across the world.
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Affiliation(s)
- Brandon P Hedrick
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York, USA
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4
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Directional asymmetry in gonad length indicates moray eels (Teleostei, Anguilliformes, Muraenidae) are "right-gonadal". Sci Rep 2023; 13:2963. [PMID: 36807600 PMCID: PMC9941099 DOI: 10.1038/s41598-023-29218-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Accepted: 01/31/2023] [Indexed: 02/22/2023] Open
Abstract
Directional asymmetry indicates a unidirectional deviation from perfect bilateral symmetry, which was rarely examined in the inner organs of the teleost (Teleostei) compared to external traits. This study examines the directional asymmetry in the gonad length of 20 species of moray eels (Muraenidae) and two outgroup species with 2959 individuals. We tested three hypotheses: (1) moray eel species did not exhibit directional asymmetry in the gonad length; (2) the directional asymmetry pattern was the same for all selected species; (3) the directional asymmetry was not related to the major habitat types, depth and size classes, and taxonomic closeness of the species. Moray eels were generally "right-gonadal", the right gonad length being constantly and significantly longer than the left one in all studied Muraenidae species. The degree of asymmetry varied among species and was not significantly related to taxonomic closeness. The habitat types, depth, and size classes had intermingled effects on observed asymmetry without a clear correspondence. The directional asymmetry in the gonad length is a unique and widely occurring phenomenon in the Family Muraenidae, which was likely a by-product in the evolutionary history without significant disadvantage in survival.
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5
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Clark CJ, Hutchinson JR, Garland T. The Inverse Krogh Principle: All Organisms Are Worthy of Study. Physiol Biochem Zool 2023; 96:1-16. [PMID: 36626844 DOI: 10.1086/721620] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
AbstractKrogh's principle states, "For such a large number of problems there will be some animal of choice, or a few such animals, on which it can be most conveniently studied." The downside of picking a question first and then finding an ideal organism on which to study it is that it will inevitably leave many organisms neglected. Here, we promote the inverse Krogh principle: all organisms are worthy of study. The inverse Krogh principle and the Krogh principle are not opposites. Rather, the inverse Krogh principle emphasizes a different starting point for research: start with a biological unit, such as an organism, clade, or specific organism trait, then seek or create tractable research questions. Even the hardest-to-study species have research questions that can be asked of them: Where does it fall within the tree of life? What resources does it need to survive and reproduce? How does it differ from close relatives? Does it have unique adaptations? The Krogh and inverse Krogh approaches are complementary, and many research programs naturally include both. Other considerations for picking a study species include extreme species, species informative for phylogenetic analyses, and the creation of models when a suitable species does not exist. The inverse Krogh principle also has pitfalls. A scientist that picks the organism first might choose a research question not really suited to the organism, and funding agencies rarely fund organism-centered grant proposals. The inverse Krogh principle does not call for all organisms to receive the same amount of research attention. As knowledge continues to accumulate, some organisms-models-will inevitably have more known about them than others. Rather, it urges a broader search across organismal diversity to find sources of inspiration for research questions and the motivation needed to pursue them.
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Abstract
Despite their evolutionary and biomedical importance, studies of the morphology and function of female genitalia have continued to lag behind those of male genitalia. While studying female genitalia can be difficult because of their soft, deformable and internal nature, recent advances in imaging, geometric analyses of shape and mechanical testing have been made, allowing for a much greater understanding of the incredible diversity of form and function of female genitalia. Here we summarize some of these methods, as well as discuss some big questions in the field that are beginning to be examined now, and will continue to benefit from further work, especially a comparative approach. Topics of further research include examination of the morphology of female genitalia in situ, in-depth anatomical work in many more species, studies of the interplay between natural and sexual selection in influencing features of vaginal morphology, how these diverse functions influence the mechanical properties of tissues, and studies of clitoris morphology and function across amniotes. Many other research topics related to female genitalia remain largely unexplored, and we hope that the papers in this issue will continue to inspire further research on female genitalia.
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Affiliation(s)
- Patricia L R Brennan
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
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7
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Orr TJ, Lukitsch T, Eiting TP, Brennan PLR. Testing Morphological Relationships Between Female and Male Copulatory Structures in Bats. Integr Comp Biol 2022; 62:icac040. [PMID: 35661885 DOI: 10.1093/icb/icac040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The lower reproductive tract of female mammals has several competing functions including mating, tract health maintenance, and parturition. Diverse vaginal anatomy suggests interactions between natural and sexual selection, yet despite its importance, female copulatory morphology remains under-studied. We undertook a comparative study across the species-rich mammalian order Chiroptera (bats) with a focus on the suborder Yangochiroptera (Vespertilioniformes) to examine how female vaginal features may have coevolved with male penis morphology to minimize mechanical damage to their tissues during copulation. The penis morphology is diverse, presenting great potential for post-copulatory sexual selection and coevolution with the female morphology, but vaginas have not been carefully examined. Here we test the hypotheses that vaginal thickness and collagen density have coevolved with features of the male penis including the presence of spines and a baculum. We present histological data from females of 24 species from 7 families of bats, and corresponding data on male penis anatomy. We also examine the role of phylogenetic history in the morphological patterns we observe. We found evidence that female vaginal thickness has coevolved with the presence of penile spines, but not with baculum presence or width. Collagen density did not appear to covary with male penile features. Our findings highlight the importance of considering interactions between the sexes in influencing functional reproductive structures and examine how these structures have been under selection in bats.
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Affiliation(s)
- Teri J Orr
- New Mexico State University, Department of Biology, Las Cruces, NM 88003
| | - Theresa Lukitsch
- New Mexico State University, Department of Biology, Las Cruces, NM 88003
| | - Thomas P Eiting
- Department of Neurobiology, University of Utah, Salt Lake City, UT 84112
| | - Patricia L R Brennan
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075
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8
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Clear E, Grant RA, Carroll M, Brassey CA. A Review and Case Study of 3D Imaging Modalities for Female Amniote Reproductive Anatomy. Integr Comp Biol 2022; 62:icac027. [PMID: 35536568 PMCID: PMC10570564 DOI: 10.1093/icb/icac027] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 04/20/2022] [Indexed: 11/13/2022] Open
Abstract
Recent advances in non-invasive imaging methods have revitalised the field of comparative anatomy, and reproductive anatomy has been no exception. The reproductive systems of female amniotes present specific challenges, namely their often internal "hidden" anatomy. Quantifying female reproductive systems is crucial to recognising reproductive pathologies, monitoring menstrual cycles, and understanding copulatory mechanics. Here we conduct a review of the application of non-invasive imaging techniques to female amniote reproductive anatomy. We introduce the commonly used imaging modalities of computed tomography (CT) and magnetic resonance imaging (MRI), highlighting their advantages and limitations when applied to female reproductive tissues, and make suggestions for future advances. We also include a case study of micro CT and MRI, along with their associated staining protocols, applied to cadavers of female adult stoats (Mustela erminea). In doing so, we will progress the discussion surrounding the imaging of female reproductive anatomy, whilst also impacting the fields of sexual selection research and comparative anatomy more broadly.
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Affiliation(s)
- Emma Clear
- Department of Natural Sciences, Manchester Metropolitan University, Chester St, Manchester M1 5GD, UK
- Williamson Park Zoo, Quernmore Road, Lancaster, Lancashire LA1 1UX, UK
| | - Robyn A Grant
- Department of Natural Sciences, Manchester Metropolitan University, Chester St, Manchester M1 5GD, UK
| | - Michael Carroll
- Department of Life Sciences, Manchester Metropolitan University, Chester St, Manchester M1 5GD, UK
| | - Charlotte A Brassey
- Department of Natural Sciences, Manchester Metropolitan University, Chester St, Manchester M1 5GD, UK
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9
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Frank TM, Dodson P, Hedrick BP. Form and function in the avian pelvis. J Morphol 2022; 283:875-893. [DOI: 10.1002/jmor.21479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Revised: 03/08/2022] [Accepted: 04/16/2022] [Indexed: 11/09/2022]
Affiliation(s)
- Tanner M. Frank
- Department of Integrative Biology University of California‐Berkeley Berkeley California USA
| | - Peter Dodson
- Department of Biomedical Sciences, School of Veterinary Medicine University of Pennsylvania Philadelphia Pennsylvania USA
- Department of Earth and Environmental Science, School of Arts and Sciences University of Pennsylvania Philadelphia Pennsylvania USA
| | - Brandon P. Hedrick
- Department of Cell Biology and Anatomy School of Medicine, Louisiana State University Health Sciences Center New Orleans Los Angeles USA
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10
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Greenwood JF, Granados GL, Secor SM, Todd BD, Showalter I, Hedrick BP, Brennan PLR. Divergent Genital Morphologies and Female-Male Covariation in Watersnakes. Integr Comp Biol 2022; 62:icac020. [PMID: 35512541 DOI: 10.1093/icb/icac020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Genital evolution can be driven by diverse selective pressures. Across taxa we see evidence of covariation between males and females, as well as divergent genital morphologies between closely related species. Quantitative analyses of morphological changes in coevolving male and female genitalia have not yet been shown in vertebrates. This study uses 2D and 3D geometric morphometrics to quantitatively compare the complex shapes of vaginal pouches and hemipenes across three species of watersnakes (the sister taxa Nerodia fasciata, N. sipedon, and a close relative N. rhombifer) to address the relationship between genital morphology and divergence time in a system where sexual conflict may have driven sexually antagonistic coevolution of genital traits. Our pairwise comparisons of shape differences across species show that the sister species have male and female genitalia that are significantly different from each other, but more similar to each other than to N. rhombifer. We also determine that the main axes of shape variation are the same for males and females, with changes that relate to deeper bilobation of the vaginal pouch and hemipenes. In males, the protrusion of the region of spines at the base of the hemipene trades off with the degree of bilobation, suggesting amelioration of sexual conflict, perhaps driven by changes in the relative size of the entrance of the vaginal pouch that could have made spines less effective.
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Affiliation(s)
- J F Greenwood
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075
| | - G Lara Granados
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075
| | - S M Secor
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL 35487
| | - B D Todd
- Department of Wildlife, Fish, and Conservation Biology, University of California, Davis, Davis, CA 95616
| | - I Showalter
- Biology Department, University of Massachusetts-Amherst, Amherst, MA 01003
| | - B P Hedrick
- Department of Cell Biology and Anatomy, Louisiana State University Health Sciences Center, New Orleans LA 70012
| | - P L R Brennan
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075
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11
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Orbach DN. Gender Bias in the Study of Genital Evolution: Females Continue to Receive Less Attention than Males. Integr Comp Biol 2022; 62:icac012. [PMID: 35353194 DOI: 10.1093/icb/icac012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The evolution of female genitalia has historically received less attention than male reproductive organs. Several papers have underscored the disparities in research efforts, but have calls for change resonated with the scientific community and rectified the skew? A literature review was conducted of journal articles published between 2013 through 2021 that explore genital evolution to determine if gender bias (sex of research subject) and imbalance (sex of researcher) have changed. Of the 334 articles that specifically explored genital evolution, first authors of both sexes published on female genitalia less than half as often as male genitalia, although the majority of authors published on genitalia of both sexes. First authors of both sexes mentioned females after males substantially more often than females before males. Female first authors published the most about genital evolution in all taxa except for insects and arachnids. Female first authors published in high impact journals marginally less often than male first authors. Articles about genital evolution across taxa generally had high impact factors, but how impact factors and number of citations varied by the sex of the subject was not clear. Although the number of studies exploring genital co-evolution between the sexes has increased across taxa and years, female genitalia continue to be researched less often than male genitalia when only one sex is investigated. Both female and male scientists are publishing in the field of genital evolution, although research on female subjects continue to lag behind males, demonstrating continued bias within the discipline.
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Affiliation(s)
- D N Orbach
- Department of Life Sciences, Texas A&M University- Corpus Christi
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12
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OUP accepted manuscript. Biol J Linn Soc Lond 2022. [DOI: 10.1093/biolinnean/blac051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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13
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Cardini A, de Jong YA, Butynski TM. Can morphotaxa be assessed with photographs? Estimating the accuracy of two-dimensional cranial geometric morphometrics for the study of threatened populations of African monkeys. Anat Rec (Hoboken) 2021; 305:1402-1434. [PMID: 34596361 PMCID: PMC9298422 DOI: 10.1002/ar.24787] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Revised: 08/23/2021] [Accepted: 08/26/2021] [Indexed: 11/09/2022]
Abstract
The classification of most mammalian orders and families is under debate and the number of species is likely greater than currently recognized. Improving taxonomic knowledge is crucial, as biodiversity is in rapid decline. Morphology is a source of taxonomic knowledge, and geometric morphometrics applied to two dimensional (2D) photographs of anatomical structures is commonly employed for quantifying differences within and among lineages. Photographs are informative, easy to obtain, and low cost. 2D analyses, however, introduce a large source of measurement error when applied to crania and other highly three dimensional (3D) structures. To explore the potential of 2D analyses for assessing taxonomic diversity, we use patas monkeys (Erythrocebus), a genus of large, semi-terrestrial, African guenons, as a case study. By applying a range of tests to compare ventral views of adult crania measured both in 2D and 3D, we show that, despite inaccuracies accounting for up to one-fourth of individual shape differences, results in 2D almost perfectly mirror those in 3D. This apparent paradox might be explained by the small strength of covariation in the component of shape variance related to measurement error. A rigorous standardization of photographic settings and the choice of almost coplanar landmarks are likely to further improve the correspondence of 2D to 3D shapes. 2D geometric morphometrics is, thus, appropriate for taxonomic comparisons of patas ventral crania. Although it is too early to generalize, our results corroborate similar findings from previous research in mammals, and suggest that 2D shape analyses are an effective heuristic tool for morphological investigation of small differences.
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Affiliation(s)
- Andrea Cardini
- Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Modena, Italy.,School of Anatomy, Physiology and Human Biology, The University of Western Australia, Crawley, Western Australia, Australia
| | - Yvonne A de Jong
- Eastern Africa Primate Diversity and Conservation Program and Lolldaiga Hills Research Programme, Nanyuki, Kenya
| | - Thomas M Butynski
- Eastern Africa Primate Diversity and Conservation Program and Lolldaiga Hills Research Programme, Nanyuki, Kenya
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14
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Hedrick BP, Schachner ER, Dodson P. Alligator appendicular architecture across an ontogenetic niche shift. Anat Rec (Hoboken) 2021; 305:3088-3100. [PMID: 34310868 DOI: 10.1002/ar.24717] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 05/17/2021] [Accepted: 05/20/2021] [Indexed: 01/08/2023]
Abstract
A variety of species undergo ontogenetic niche shifts in either diet, habitat, or both. As a result, multiple ontogenetic stages are able to take advantage of different resources and live in sympatry without competing with one another. The American alligator (Alligator mississippiensis) begins to undergo an ontogenetic niche shift in both diet and habitat at a length of 1.2 m. They transition from a terrestrial wetland environment to a riverine environment and take advantage of different dietary resources. At 1.8 m, A. mississippiensis reaches sexual maturity. Ontogenetic shifts in habitat have the capacity to alter morphology, especially limb morphology, as different age classes traverse different ecological systems. We evaluated shape trends in the scapulae, humeri, ilia, and femora using geometric morphometrics to test whether there were punctuated changes in limb shape, shape disparity, and integration corresponding to either the ontogenetic habitat shift or onset of sexual maturity. We found size to strongly correlate with limb shape but found a continuous size gradient rather than punctuated changes in size. Furthermore, we found that adults (total length > 1.8 m) had significantly higher limb shape disparity than juveniles or subadults, likely related to ontogenetic decreases in limb use and a reduction in limb constraints. Finally, we found that the forelimb and hindlimb acted as a single integrated unit and that neither the forelimb nor hindlimb was significantly more integrated than the other. Therefore, the ontogenetic niche shift itself did not impact limb morphology in A. mississippiensis.
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Affiliation(s)
- Brandon P Hedrick
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Science Center, New Orleans, Louisiana, USA
| | - Emma R Schachner
- Department of Cell Biology and Anatomy, School of Medicine, Louisiana State University Health Science Center, New Orleans, Louisiana, USA
| | - Peter Dodson
- Department of Biomedical Sciences, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania, USA.,Department of Earth and Environmental Science, School of Arts and Sciences, University of Pennsylvania, Philadelphia, Pennsylvania, USA
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15
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Moore BC, Kelly DA, Piva M, Does M, Kim DK, Simoncini M, Leiva PML, Pina CI. Genital anatomy and copulatory interactions in the broad snouted Caiman (Caiman latirostris). Anat Rec (Hoboken) 2021; 305:3075-3087. [PMID: 34236769 DOI: 10.1002/ar.24699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2021] [Accepted: 03/29/2021] [Indexed: 11/09/2022]
Abstract
The broad snouted caiman is a crocodylian native to South America that is subject to extensive conservation management in both wild and farming environments. Although reproductive behaviors like egg laying and clutch care have been examined in this species, little else is known about their copulatory system. We examined the anatomy of male and female cloacal and genital tissues ex vivo to build hypotheses of their interactions during copulation and the effects of that interaction on insemination. Male phallic glans tissues were artificially inflated to expand into their copulatory state, allowing the examination and quantification of structural changes at the gross and tissue levels. Digital reconstruction of MRI stacks yielded three-dimensional tissue compartment specific glans models of the inflated state. Silicone molds of female cloacae and oviducts in conjunction with dissection and diceCT analysis allowed us to assess internal geometry and infer how male and female features interact in copulo. We observed glans expansion within the female proctodeum would result in a copulatory lock limiting deeper intromission or retraction. Intromission and subsequent creation of the copulatory lock produces extensive clitoral compression, providing a possible mechanism for female assessment of male copulatory performance. Further, glans expansion forms a distal lumen that positions the glans tip in or near the vaginal openings. A coiled, muscular vagina provides a possible mechanism for postcopulatory sexual selection by excluding semen. Together, the complex male-female interaction supports evidence for cryptic selection by female choice, which can act as a driver of genital coevolution.
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Affiliation(s)
- Brandon C Moore
- Department of Biomedical Science, College of Veterinary Medicine, University of Missouri, Columbia, Missouri, USA.,Deartment of Biology, School of Health Sciences, Stephens College, Columbia, Missouri, USA
| | - Diane A Kelly
- Department of Psychological and Brain Sciences, University of Massachusetts, Amherst, Massachusetts, USA
| | - Milan Piva
- Department of Biomedical Science, College of Veterinary Medicine, University of Missouri, Columbia, Missouri, USA
| | - Mark Does
- Department of Biomedical Engineering, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Dong Kyu Kim
- Department of Biomedical Engineering, Vanderbilt University School of Medicine, Nashville, Tennessee, USA
| | - Melina Simoncini
- CICyTTP (CONICET-Prov. ER-UADER), Proyecto Yacare, FCYT/UADER, Diamante, Entre Ríos, Argentina
| | - Pamela M L Leiva
- CICyTTP (CONICET-Prov. ER-UADER), Proyecto Yacare, FCYT/UADER, Diamante, Entre Ríos, Argentina
| | - Carlos I Pina
- CICyTTP (CONICET-Prov. ER-UADER), Proyecto Yacare, FCYT/UADER, Diamante, Entre Ríos, Argentina
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16
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Brennan PLR, Sterett M, DiBuono M, Lara Granados G, Klo K, Marsden R, Schleinig P, Tanner L, Purdy S. Intra-horn Penile Intromission in the Alpaca Vicugna pacos and Consequences to Genital Morphology. Integr Comp Biol 2021; 61:624-633. [PMID: 33970265 DOI: 10.1093/icb/icab050] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Copulatory behavior and genital morphology interact to deliver sperm more effectively during mating, but the nature of this interaction has not been explored in depth in most vertebrates. Alpacas have unusually long copulations lasting 15-20 min, and a unique copulatory behavior, where the penis intromits all the way past the cervix, into the uterine horns. Here we describe the morphology of male and female genitalia and report unique morphological characteristics that may be associated with this unusual insemination mode. Vaginal shape is highly variable, and seemingly not associated with age or parity. The cranial vagina varies between bulbous and cylindrical, while the caudal vagina is typically narrower and always cylindrical. The cervix consists of a series of two to three spirals or rings, and it is often found in a relaxed state that may prevent damage caused by the cartilaginous penis tip as it pushes through the cervix to reach the uterine horns. The uterus and uterine horns have a complex shape with multiple constrictions. The cartilaginous penis tip has a sharp urethral process that may help to push against these constrictions. The diameter of the vaginal lumen is much greater than the diameter of the penis suggesting that there is little direct interaction between them, and that female vaginal shape is not under strong copulatory selection. In effect, the entire female reproductive tract of the female is interacting with the penis during copulation.
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Affiliation(s)
- Patricia L R Brennan
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Maya Sterett
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Mary DiBuono
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Genesis Lara Granados
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Kay Klo
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Rebecca Marsden
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Pearl Schleinig
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Louise Tanner
- Department of Biological Sciences, Mount Holyoke College, South Hadley, MA 01075, USA
| | - Stephen Purdy
- North American Camelid Studies Program, Nunoa Project, Belchertown, MA 01007, USA
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17
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Orbach DN, Brassey CA, Gardiner JD, Brennan PLR. 3D genital shape complexity in female marine mammals. Ecol Evol 2021; 11:3210-3218. [PMID: 33841778 PMCID: PMC8019040 DOI: 10.1002/ece3.7269] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 12/17/2020] [Accepted: 01/12/2021] [Indexed: 11/06/2022] Open
Abstract
Comparisons of 3D shapes have recently been applied to diverse anatomical structures using landmarking techniques. However, discerning evolutionary patterns can be challenging for structures lacking homologous landmarks. We used alpha shape analyses to quantify vaginal shape complexity in 40 marine mammal specimens including cetaceans, pinnipeds, and sirenians. We explored phylogenetic signal and the potential roles of natural and sexual selection on vaginal shape evolution. Complexity scores were consistent with qualitative observations. Cetaceans had a broad range of alpha complexities, while pinnipeds were comparatively simple and sirenians were complex. Intraspecific variation was found. Three-dimensional surface heat maps revealed that shape complexity was driven by invaginations and protrusions of the vaginal wall. Phylogenetic signal was weak and metrics of natural selection (relative neonate size) and sexual selection (relative testes size, sexual size dimorphism, and penis morphology) did not explain vaginal complexity patterns. Additional metrics, such as penile shape complexity, may yield interesting insights into marine mammal genital coevolution. We advocate for the use of alpha shapes to discern patterns of evolution that would otherwise not be possible in 3D anatomical structures lacking homologous landmarks.
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Affiliation(s)
- Dara N. Orbach
- Department of Life SciencesTexas A&M University‐ Corpus ChristiCorpus ChristiTXUSA
- Department of Biological SciencesMount Holyoke CollegeSouth HadleyMAUSA
| | - Charlotte A. Brassey
- School of Science and the EnvironmentManchester Metropolitan UniversityManchesterUK
| | - James D. Gardiner
- Department of Musculoskeletal and Ageing ScienceInstitute of Lifecourse and Medical SciencesUniversity of LiverpoolLiverpoolUK
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18
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Conith AJ, Hope SA, Chhouk BH, Albertson RC. Weak genetic signal for phenotypic integration implicates developmental processes as major regulators of trait covariation. Mol Ecol 2021; 30:464-480. [PMID: 33231336 PMCID: PMC8811731 DOI: 10.1111/mec.15748] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Revised: 11/03/2020] [Accepted: 11/04/2020] [Indexed: 12/30/2022]
Abstract
Phenotypic integration is an important metric that describes the degree of covariation among traits in a population, and is hypothesized to arise due to selection for shared functional processes. Our ability to identify the genetic and/or developmental underpinnings of integration is marred by temporally overlapping cell-, tissue- and structure-level processes that serve to continually 'overwrite' the structure of covariation among traits through ontogeny. Here, we examine whether traits that are integrated at the phenotypic level also exhibit a shared genetic basis (e.g. pleiotropy). We micro-CT scanned two hard tissue traits, and two soft tissue traits (mandible, pectoral girdle, atrium and ventricle, respectively) from an F5 hybrid population of Lake Malawi cichlids, and used geometric morphometrics to extract 3D shape information from each trait. Given the large degree of asymmetric variation that may reflect developmental instability, we separated symmetric from asymmetric components of shape variation. We then performed quantitative trait loci (QTL) analysis to determine the degree of genetic overlap between shapes. While we found ubiquitous associations among traits at the phenotypic level, except for a handful of notable exceptions, our QTL analysis revealed few overlapping genetic regions. Taken together, this indicates developmental interactions can play a large role in determining the degree of phenotypic integration among traits, and likely obfuscate the genotype to phenotype map, limiting our ability to gain a comprehensive picture of the genetic contributors responsible for phenotypic divergence.
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Affiliation(s)
- Andrew J. Conith
- Biology Department, University of Massachusetts Amherst, Amherst, MA, 01002
| | - Sylvie A. Hope
- Biology Department, University of Massachusetts Amherst, Amherst, MA, 01002
| | - Brian H Chhouk
- Biology Department, University of Massachusetts Amherst, Amherst, MA, 01002
| | - R. Craig Albertson
- Biology Department, University of Massachusetts Amherst, Amherst, MA, 01002
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19
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Dziomber L, Joyce WG, Foth C. The ecomorphology of the shell of extant turtles and its applications for fossil turtles. PeerJ 2020; 8:e10490. [PMID: 33391873 PMCID: PMC7761203 DOI: 10.7717/peerj.10490] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2020] [Accepted: 11/13/2020] [Indexed: 11/20/2022] Open
Abstract
Turtles are a successful clade of reptiles that originated in the Late Triassic. The group adapted during its evolution to different types of environments, ranging from dry land to ponds, rivers, and the open ocean, and survived all Mesozoic and Cenozoic extinction events. The body of turtles is characterized by a shell, which has been hypothesized to have several biological roles, like protection, thermal and pH regulation, but also to be adapted in its shape to the ecology of the animal. However, only few studies have investigated the relationships between shell shape and ecology in a global context or clarified if shape can be used to diagnose habitat preferences in fossil representatives. Here, we assembled a three-dimensional dataset of 69 extant turtles and three fossils, in particular, the Late Triassic Proganochelys quenstedtii and Proterochersis robusta and the Late Jurassic Plesiochelys bigleri to test explicitly for a relationship between shell shape and ecology. 3D models were obtained using surface scanning and photogrammetry. The general shape of the shells was captured using geometric morphometrics. The habitat ecology of extant turtles was classified using the webbing of their forelimbs as a proxy. Principal component analysis (PCA) highlights much overlap between habitat groups. Discriminant analyses suggests significant differences between extant terrestrial turtles, extant fully aquatic (i.e., marine and riverine) turtles, and an unspecialized assemblage that includes extant turtles from all habitats, mostly freshwater aquatic forms. The paleoecology of the three fossil species cannot be determined with confidence, as all three fall within the unspecialized category, even if Plesiochelys bigleri plots closer to fully aquatic turtles, while the two Triassic species group closer to extant terrestrial forms. Although the shape of the shell of turtles indeed contains an ecological signal, it is overall too weak to uncover using shell shape in paleoecological studies, at least with the methods we selected.
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Affiliation(s)
- Laura Dziomber
- Department of Geosciences, University of Fribourg, Fribourg, Switzerland
- Institute of Plant Sciences & Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
| | - Walter G. Joyce
- Department of Geosciences, University of Fribourg, Fribourg, Switzerland
| | - Christian Foth
- Department of Geosciences, University of Fribourg, Fribourg, Switzerland
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20
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Brassey CA, Behnsen J, Gardiner JD. Postcopulatory sexual selection and the evolution of shape complexity in the carnivoran baculum. Proc Biol Sci 2020; 287:20201883. [PMID: 33049172 PMCID: PMC7657853 DOI: 10.1098/rspb.2020.1883] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
The baculum is an enigmatic bone within the mammalian glans penis, and the driving forces behind its often bizarre shape have captivated evolutionary biologists for over a century. Hypotheses for the function of the baculum include aiding in intromission, stimulating females and assisting with prolonged mating. Previous attempts to test these hypotheses have focused on the gross size of the baculum and have failed to reach a consensus. We conducted three-dimensional imaging and apply a new method to quantify three-dimensional shape complexity in the carnivoran baculum. We show that socially monogamous species are evolving towards complex-shaped bacula, whereas group-living species are evolving towards simple bacula. Overall three-dimensional baculum shape complexity is not related to relative testes mass, but tip complexity is higher in induced ovulators and species engaging in prolonged copulation. Our study provides evidence of postcopulatory sexual selection pressures driving three-dimensional shape complexity in the carnivore baculum.
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Affiliation(s)
- Charlotte A Brassey
- Department of Natural Sciences, Manchester Metropolitan University, M1 5GD, UK
| | - Julia Behnsen
- Manchester X-ray Imaging Facility, University of Manchester, M13 9PL, UK
| | - James D Gardiner
- Institute of Ageing and Chronic Disease, University of Liverpool, L7 8TX, UK
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21
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Wasiljew BD, Pfaender J, Wipfler B, Utama IV, Herder F. Do we need the third dimension? Quantifying the effect of the z-axis in 3D geometric morphometrics based on sailfin silversides (Telmatherinidae). JOURNAL OF FISH BIOLOGY 2020; 97:537-545. [PMID: 32447773 DOI: 10.1111/jfb.14410] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Revised: 05/14/2020] [Accepted: 05/21/2020] [Indexed: 06/11/2023]
Abstract
This study investigated the impact of the third dimension in geometric morphometrics (GM) using sailfin silversides (Telmatherinidae) from the Malili Lakes of Sulawesi (Indonesia). The three morphospecies of the monophyletic "roundfin" radiation are laterally compressed and vary in shape traits. The results of 2D and 3D GM were compared and quantified to discuss the advantages and disadvantages of both methods for closely related species and their sexes. This approach focused on the head because it is far more complex and three-dimensionally structured than the trunk or the caudal region. The results revealed no significant benefit concerning repeatability and measurement error in 3D GM compared to 2D GM. The z-axis contributed substantially to the variance of the 3D data set but was irrelevant for discrimination of species and sexes in the approach. Limited gain in information was contrasted by substantially higher effort for 3D compared to the 2D analyses. The study concluded that 2D GM is the more efficient shape analysis approach for discriminating roundfins. Broader studies are needed to test which of the two methods is more efficient in distinguishing laterally compressed fishes in general. For future studies, due to the high investment required, this study recommends carefully evaluating the necessity of 3D GM. If in doubt, this study suggests testing for congruence between 2D and 3D GM with a subsample and consequently applying 2D GM in the case of high congruence.
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Affiliation(s)
- Benjamin D Wasiljew
- Sektion Ichthyologie, Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany
| | - Jobst Pfaender
- Ichthyologie, Naturkundemuseum Potsdam, Potsdam, Germany
| | - Benjamin Wipfler
- Sektion Ichthyologie, Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany
| | - Ilham Vemandra Utama
- Ichthyology Laboratory, Division of Zoology, Research Center for Biology, Indonesian Institute of Sciences (LIPI), Bogor, Indonesia
| | - Fabian Herder
- Sektion Ichthyologie, Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany
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22
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Orbach DN, Brennan PLR, Hedrick BP, Keener W, Webber MA, Mesnick SL. Asymmetric and Spiraled Genitalia Coevolve with Unique Lateralized Mating Behavior. Sci Rep 2020; 10:3257. [PMID: 32094449 PMCID: PMC7039966 DOI: 10.1038/s41598-020-60287-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 02/10/2020] [Indexed: 02/04/2023] Open
Abstract
Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Phocoena phocoena). Males attempt copulation by approaching a female exclusively on her left side. To understand if this unusual lateralized behavior may have coevolved with genital morphology, we quantified the shape of female and male harbor porpoise reproductive tracts using 2D geometric morphometrics and 3D models of the vaginal lumen and inflated distal penis. We found that the vaginas varied individually in shape and that the vaginas demonstrated both significant directional and fluctuating asymmetry. This asymmetry resulted from complex 3D spirals and vaginal folds with deep recesses, which may curtail the depth or direction of penile penetration and/or semen movement. The asymmetric shapes of the vaginal lumen and penis tip were both left-canted with similar angular bends that mirrored one another and correspond with the left lateral mating approach. We suggest that the reproductive anatomy of both sexes and their lateral mating behavior coevolved.
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Affiliation(s)
- Dara N Orbach
- Texas A&M University- Corpus Christi, Department of Life Sciences, 6300 Ocean Dr., Corpus Christi, Texas, 78412, USA. .,Mount Holyoke College, Department of Biological Sciences, 50 College Street, South Hadley, Massachusetts, 01075, USA.
| | - Patricia L R Brennan
- Mount Holyoke College, Department of Biological Sciences, 50 College Street, South Hadley, Massachusetts, 01075, USA
| | - Brandon P Hedrick
- Louisiana State University Health Sciences Center, Department of Cell Biology and Anatomy, 1901 Perdido Street, New Orleans, LA, 70112, USA.,University of Oxford, Department of Earth Sciences, South Parks Road, Oxford, OX1 3AN, UK
| | - William Keener
- The Marine Mammal Center, 2000 Bunker Road, Sausalito, California, 94965, USA
| | - Marc A Webber
- The Marine Mammal Center, 2000 Bunker Road, Sausalito, California, 94965, USA
| | - Sarah L Mesnick
- Marine Mammal and Turtle Division, Southwest Fisheries Science Center, National Marine Fisheries Service, National Oceanic and Atmospheric Administration, 8901 La Jolla Shores Drive, La Jolla, California, 92037, USA
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23
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Cardini A, Chiapelli M. How flat can a horse be? Exploring 2D approximations of 3D crania in equids. ZOOLOGY 2020; 139:125746. [PMID: 32086141 DOI: 10.1016/j.zool.2020.125746] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 01/15/2020] [Accepted: 01/16/2020] [Indexed: 01/13/2023]
Abstract
Quantitative analyses of morphological variation using geometric morphometrics are often performed on 2D photos of 3D structures. It is generally assumed that the error due to the flattening of the third dimension is negligible. However, despite hundreds of 2D studies, few have actually tested this assumption and none has done it on large animals, such as those typically classified as megafauna. We explore this issue in living equids, focusing on ventral cranial variation at both micro- and macro-evolutionary levels. By comparing 2D and 3D data, we found that size is well approximated, whereas shape is more strongly impacted by 2D inaccuracies, as it is especially evident in intra-specific analyses. The 2D approximation improves when shape differences are larger, as in macroevolution, but even at this level precise inter-individual similarity relationships are altered. Despite this, main patterns of sex, species and allometric variation in 2D were the same as in 3D, thus suggesting that 2D may be a source of 'noise' that does not mask the main signal in the data. However, the picture that emerges from this and other recent studies on 2D approximation of 3D structures is complex and any generalization premature. Morphometricians should therefore test the appropriateness of 2D using preliminary investigations in relation to the specific study questions in their own samples. We discuss whether this might be feasible using a reduced landmark configuration and smaller samples, which would save time and money. In an exploratory analysis, we found that in equids results seem robust to sampling, but become less precise and, with fewer landmarks, may slightly overestimate 2D inaccuracies.
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Affiliation(s)
- Andrea Cardini
- Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Via Campi 103, 41125, Modena, Italy; Centre for Forensic Anatomy and Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia.
| | - Marika Chiapelli
- Dipartimento di Scienze Chimiche e Geologiche, Università di Modena e Reggio Emilia, Via Campi 103, 41125, Modena, Italy
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24
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Ribeiro JRI, Stefanello F, Bugs C, Stenert C, Maltchik L, Guilbert E. Coevolution between male and female genitalia in Belostoma angustum Lauck, 1964 (Insecta, Heteroptera, Belostomatidae): disentangling size and shape. ZOOLOGY 2019; 137:125711. [PMID: 31634693 DOI: 10.1016/j.zool.2019.125711] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2019] [Revised: 08/03/2019] [Accepted: 09/22/2019] [Indexed: 11/26/2022]
Abstract
Sexual and natural selection mechanisms might drive variation in the genitalia of male animals. All aforementioned mechanisms are known to predict the coevolution of male and female genital morphology. Belostoma angustum is known to have subtle variation in the male and female genitalia of its members. In this species, phallosoma with dorsal arms and ventral diverticulum are assumed to be intromittent male genital traits that interact with the female genital chamber. We thus evaluated the existence of variation after disentangling the size from the shape of male genitalia in B. angustum. Body and genitalia dimensions and photographs of phallosoma with dorsal arms, ventral diverticulum and lateral views of the right paramere (the non-intromittent part) were obtained. Semi-landmarks and landmarks were used to capture phenotypic variation, by eliminating all non-shape variation with a Procrustes superimposition. Male and female specimens collected from the same location or immediate vicinity were grouped, and 12 groups originating from 12 locations were used to conduct two block-Partial Least Squares analyses (PLS). Group structures were also taken into account by adopting a multilevel approach. The male and female genital traits had similarly shallow static allometry slopes, as well as the dispersion values around the mean (i.e. coefficient of variation) and the standard error of the estimate. The correlation between the pooled within-locality covariance matrix of the symmetric component of phallosoma with dorsal arms and the female genital chamber was significant (r-PLS=0.37), as well as that with male body dimensions (r-PLS=0.36), even after controlling for allometry. Specimens with lower PLS shape scores had narrower phallosoma with dorsal arms, with poorly curved outer margins of the dorsal arms, whereas specimens with higher PLS shape scores had slightly shorter dorsal arms, with strongly curved outer margins. Lower shape scores were associated with narrower and especially shorter and narrower female genital chambers. Similar shallow allometric curves among sexes and the correlation between intromittent male parts and the female genital chamber, as well as male dimensions, suggest the coevolution of these contact structures in size and in shape.
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Affiliation(s)
- José Ricardo Inacio Ribeiro
- Laboratório de Estudos da Biodiversidade do Pampa (LEBIP), Universidade Federal do Pampa, Campus São Gabriel, 97307-020, São Gabriel, Rio Grande do Sul State, Brazil.
| | - Fabiano Stefanello
- Laboratório de Estudos da Biodiversidade do Pampa (LEBIP), Universidade Federal do Pampa, Campus São Gabriel, 97307-020, São Gabriel, Rio Grande do Sul State, Brazil.
| | - Cristhian Bugs
- Laboratório de Estudos da Biodiversidade do Pampa (LEBIP), Universidade Federal do Pampa, Campus São Gabriel, 97307-020, São Gabriel, Rio Grande do Sul State, Brazil.
| | - Cristina Stenert
- Laboratório de Ecologia e Conservação de Ecossistemas Aquáticos, Universidade do Vale do Rio dos Sinos, Av. Unisinos, 950, 93022-000, Cristo Rei, São Leopoldo, Rio Grande do Sul State, Brazil.
| | - Leonardo Maltchik
- Laboratório de Ecologia e Conservação de Ecossistemas Aquáticos, Universidade do Vale do Rio dos Sinos, Av. Unisinos, 950, 93022-000, Cristo Rei, São Leopoldo, Rio Grande do Sul State, Brazil.
| | - Eric Guilbert
- Muséum national d'Histoire naturelle, MECADEV - UMR 7179 MNHN/CNRS, CP50-57, rue Cuvier, 75005, Paris, France.
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25
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Sloan NS, Simmons LW. The evolution of female genitalia. J Evol Biol 2019; 32:882-899. [PMID: 31267594 DOI: 10.1111/jeb.13503] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 06/14/2019] [Accepted: 06/21/2019] [Indexed: 02/07/2023]
Abstract
Female genitalia have been largely neglected in studies of genital evolution, perhaps due to the long-standing belief that they are relatively invariable and therefore taxonomically and evolutionarily uninformative in comparison with male genitalia. Contemporary studies of genital evolution have begun to dispute this view, and to demonstrate that female genitalia can be highly diverse and covary with the genitalia of males. Here, we examine evidence for three mechanisms of genital evolution in females: species isolating 'lock-and-key' evolution, cryptic female choice and sexual conflict. Lock-and-key genital evolution has been thought to be relatively unimportant; however, we present cases that show how species isolation may well play a role in the evolution of female genitalia. Much support for female genital evolution via sexual conflict comes from studies of both invertebrate and vertebrate species; however, the effects of sexual conflict can be difficult to distinguish from models of cryptic female choice that focus on putative benefits of choice for females. We offer potential solutions to alleviate this issue. Finally, we offer directions for future studies in order to expand and refine our knowledge surrounding female genital evolution.
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Affiliation(s)
- Nadia S Sloan
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, Western Australia, Australia
| | - Leigh W Simmons
- Centre for Evolutionary Biology, School of Biological Sciences (M092), The University of Western Australia, Crawley, Western Australia, Australia
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