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Merchant HN, Ivanova A, Hart DW, García C, Bennett NC, Portugal SJ, Faulkes CG. Patterns of Genetic Diversity and Gene Flow Associated With an Aridity Gradient in Populations of Common Mole-rats, Cryptomys hottentotus hottentotus. Genome Biol Evol 2024; 16:evae144. [PMID: 38953183 PMCID: PMC11258414 DOI: 10.1093/gbe/evae144] [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: 01/11/2024] [Revised: 05/30/2024] [Accepted: 06/25/2024] [Indexed: 07/03/2024] Open
Abstract
Genetic adaptation is the change of a population toward a phenotype that best fits the present ecological conditions of the environment it inhabits. As environmental conditions change, allele frequencies shift, resulting in different populations of the same species possessing genetic variation and divergent phenotypes. Cooperatively breeding common mole-rats (Cryptomys hottentotus hottentotus) inhabit environments along an aridity gradient in South Africa, which provides an opportunity for local genetic adaptations to occur. Using one mitochondrial gene (cytochrome b) and 3,540 SNP loci across the whole genome, we determined the phylogenetic relationship, population structure and genetic diversity of five populations of C. h. hottentotus located along an aridity gradient. Mitochondrial data identified population-specific clades that were less distinct in the two mesic populations, potentially indicating historical or recent gene flow, or the retention of ancestral haplotypes. Arid and semi-arid populations formed a distinct cluster from the non-arid populations. Genetic diversity and gene flow were higher in arid-dwelling individuals, suggesting greater connectivity and interactions between colonies in arid regions in comparison to mesic ones. Using an Aridity Index, we determined that isolation by environment, rather than isolation by geographical distance, best explains the genetic distance between the populations. Further analyses using target loci may determine if there are differing underlying genetic adaptations among populations of C. h. hottentotus. These analyses could help unravel population differences in response to environmental factors within a subspecies of bathyergid mole-rat and determine the adaptive capacity of this small nonmigratory subterranean rodent species in response to aridification in the face of climate change.
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Affiliation(s)
- Hana N Merchant
- Department of Biological Sciences, School of Life and Environmental Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
- School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK
| | - Anastasia Ivanova
- School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK
| | - Daniel W Hart
- Department of Zoology and Entomology, University of Pretoria, Pretoria, Gauteng, South Africa
| | - Cristina García
- Department of Biological Sciences, School of Life and Environmental Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
| | - Nigel C Bennett
- Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, Gauteng, South Africa
| | - Steven J Portugal
- Department of Biological Sciences, School of Life and Environmental Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK
- Department of Biology, University of Oxford, Oxford OX1 3SZ, UK
| | - Chris G Faulkes
- School of Biological and Behavioural Sciences, Queen Mary University of London, London, UK
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2
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Ruby JG, Smith M, Buffenstein R. Five years later, with double the demographic data, naked mole-rat mortality rates continue to defy Gompertzian laws by not increasing with age. GeroScience 2024:10.1007/s11357-024-01201-4. [PMID: 38773057 DOI: 10.1007/s11357-024-01201-4] [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: 04/19/2024] [Accepted: 05/09/2024] [Indexed: 05/23/2024] Open
Abstract
The naked mole-rat (Heterocephalus glaber) is a mouse-sized rodent species, notable for its eusociality and long lifespan. Previously, we reported that demographic aging, i.e., the exponential increase of mortality hazard that accompanies advancing age in mammals and other organisms, does not occur in naked mole-rats (Ruby et al., 2018), a finding that has potential implications for human healthy aging. The demographic data supporting that conclusion had taken over three decades to accumulate, starting with the original rearing of H. glaber in captivity. This finding was controversial since many of the animals in that study were relatively young. In the 5 years following that study, we have doubled our quantity of demographic data. Here, we re-evaluated our prior conclusions in light of these new data and found them to be not only supported but indeed strengthened. We additionally provided insight into the social dynamics of captive H. glaber with data and analyses of body weight and colony size versus mortality. Finally, we provide a phylogenetically proximal comparator in the form of lifespan data from our Damaraland mole-rat (Fukomys damarensis) colony and demographic meta-analysis of those data along with published data from Ansell's mole-rat (Fukomys anselli). We found Fukomys mortality hazard to increase gradually with age, an observation with inferences on the evolution of exceptional lifespan among mole-rats and the ecological factors that may have accompanied that evolution.
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Affiliation(s)
- J Graham Ruby
- Calico Life Sciences LLC, 1170 Veterans Blvd, South San Francisco, CA, 94080, USA
| | - Megan Smith
- Calico Life Sciences LLC, 1170 Veterans Blvd, South San Francisco, CA, 94080, USA
| | - Rochelle Buffenstein
- Calico Life Sciences LLC, 1170 Veterans Blvd, South San Francisco, CA, 94080, USA.
- Department of Biological Sciences, University of Illinois, Chicago 845 W Taylor, Chicago, IL, 60607, USA.
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3
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Thorley J, Bensch HM, Finn K, Clutton-Brock T, Zöttl M. Damaraland mole-rats do not rely on helpers for reproduction or survival. Evol Lett 2023; 7:203-215. [PMID: 37475748 PMCID: PMC10355180 DOI: 10.1093/evlett/qrad023] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 03/23/2023] [Accepted: 05/05/2023] [Indexed: 07/22/2023] Open
Abstract
In eusocial invertebrates and obligate cooperative breeders, successful reproduction is dependent on assistance from non-breeding group members. Although naked (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis) are often described as eusocial and their groups are suggested to resemble those of eusocial insects more closely than groups of any other vertebrate, the extent to which breeding individuals benefit from the assistance of non-breeding group members is unclear. Here we show that, in wild Damaraland mole-rats, prospective female breeders usually disperse and settle alone in new burrow systems where they show high survival rates and remain in good body condition-often for several years-before being joined by males. In contrast to many obligate cooperative vertebrates, pairs reproduced successfully without non-breeding helpers, and the breeding success of experimentally formed pairs was similar to that of larger, established groups. Though larger breeding groups recruited slightly more pups than smaller groups, adult survival was independent of group size and group size had mixed effects on the growth of non-breeders. Our results suggest that Damaraland mole-rats do not need groups to survive and that cooperative breeding in the species is not obligate as pairs can-and frequently do-reproduce without the assistance of helpers. While re-emphasizing the importance of ecological constraints on dispersal in social mole-rats, the mixed effects of group size in our study suggest that indirect benefits accrued through cooperative behavior may have played a less prominent role in the evolution of mole-rat group-living than previously thought.
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Affiliation(s)
- Jack Thorley
- Corresponding author: Department of Zoology, Downing Street, University of Cambridge, Cambridge, CB2 3EJ, United Kingdom.
| | | | - Kyle Finn
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Tim Clutton-Brock
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Zoology and Entomology, Mammal Research Institute, University of Pretoria, Pretoria, South Africa
| | - Markus Zöttl
- Kalahari Research Centre, Kuruman River Reserve, Van Zylsrus, South Africa
- Department of Biology and Environmental Science, Linnaeus University, Kalmar, Sweden
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4
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Yao B, An K, Kang Y, Tan Y, Zhang D, Su J. Reproductive Suppression Caused by Spermatogenic Arrest: Transcriptomic Evidence from a Non-Social Animal. Int J Mol Sci 2023; 24:ijms24054611. [PMID: 36902039 PMCID: PMC10003443 DOI: 10.3390/ijms24054611] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 02/12/2023] [Accepted: 02/17/2023] [Indexed: 03/02/2023] Open
Abstract
Reproductive suppression is an adaptive strategy in animal reproduction. The mechanism of reproductive suppression has been studied in social animals, providing an essential basis for understanding the maintenance and development of population stability. However, little is known about it in solitary animals. The plateau zokor is a dominant, subterranean, solitary rodent in the Qinghai-Tibet Plateau. However, the mechanism of reproductive suppression in this animal is unknown. We perform morphological, hormonal, and transcriptomic assays on the testes of male plateau zokors in breeders, in non-breeders, and in the non-breeding season. We found that the testes of non-breeders are smaller in weight and have lower serum testosterone levels than those of breeders, and the mRNA expression levels of the anti-Müllerian hormone (AMH) and its transcription factors are significantly higher in non-breeder testes. Genes related to spermatogenesis are significantly downregulated in both meiotic and post-meiotic stages in non-breeders. Genes related to the meiotic cell cycle, spermatogenesis, flagellated sperm motility, fertilization, and sperm capacitation are significantly downregulated in non-breeders. Our data suggest that high levels of AMH may lead to low levels of testosterone, resulting in delayed testicular development, and physiological reproductive suppression in plateau zokor. This study enriches our understanding of reproductive suppression in solitary mammals and provides a basis for the optimization of managing this species.
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Affiliation(s)
- Baohui Yao
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
| | - Kang An
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
| | - Yukun Kang
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
| | - Yuchen Tan
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
| | - Degang Zhang
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
| | - Junhu Su
- College of Grassland Science, Key Laboratory of Grassland Ecosystem (Ministry of Education), Gansu Agricultural University, Lanzhou 730070, China
- Massey University Research Centre for Grassland Biodiversity, Gansu Agricultural University, Lanzhou 730070, China
- Correspondence:
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5
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Brieño-Enríquez MA, Faykoo-Martinez M, Goben M, Grenier JK, McGrath A, Prado AM, Sinopoli J, Wagner K, Walsh PT, Lopa SH, Laird DJ, Cohen PE, Wilson MD, Holmes MM, Place NJ. Postnatal oogenesis leads to an exceptionally large ovarian reserve in naked mole-rats. Nat Commun 2023; 14:670. [PMID: 36810851 PMCID: PMC9944903 DOI: 10.1038/s41467-023-36284-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2020] [Accepted: 01/24/2023] [Indexed: 02/24/2023] Open
Abstract
In the long-lived naked mole-rat (NMR), the entire process of oogenesis occurs postnatally. Germ cell numbers increase significantly in NMRs between postnatal days 5 (P5) and P8, and germs cells positive for proliferation markers (Ki-67, pHH3) are present at least until P90. Using pluripotency markers (SOX2 and OCT4) and the primordial germ cell (PGC) marker BLIMP1, we show that PGCs persist up to P90 alongside germ cells in all stages of female differentiation and undergo mitosis both in vivo and in vitro. We identified VASA+ SOX2+ cells at 6 months and at 3-years in subordinate and reproductively activated females. Reproductive activation was associated with proliferation of VASA+ SOX2+ cells. Collectively, our results suggest that highly desynchronized germ cell development and the maintenance of a small population of PGCs that can expand upon reproductive activation are unique strategies that could help to maintain the NMR's ovarian reserve for its 30-year reproductive lifespan.
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Affiliation(s)
- Miguel Angel Brieño-Enríquez
- Magee-Womens Research Institute, Department of Obstetrics, Gynecology & Reproductive Sciences, University of Pittsburgh, Pittsburgh, PA, USA.
- Aging Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
| | - Mariela Faykoo-Martinez
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
- Department of Psychology, University of Toronto, Mississauga, Mississauga, ON, Canada
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON, Canada
| | - Meagan Goben
- Magee-Womens Research Institute, Department of Obstetrics, Gynecology & Reproductive Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Jennifer K Grenier
- RNA sequencing core and Center for Reproductive Genomics, College of Veterinary, Cornell University, Ithaca, NY, USA
| | - Ashley McGrath
- Department of Population Medicine & Diagnostic Sciences, Cornell University, Ithaca, NY, USA
| | - Alexandra M Prado
- Department of Population Medicine & Diagnostic Sciences, Cornell University, Ithaca, NY, USA
| | - Jacob Sinopoli
- Department of Population Medicine & Diagnostic Sciences, Cornell University, Ithaca, NY, USA
| | - Kate Wagner
- Department of Population Medicine & Diagnostic Sciences, Cornell University, Ithaca, NY, USA
| | - Patrick T Walsh
- Magee-Womens Research Institute, Department of Obstetrics, Gynecology & Reproductive Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Samia H Lopa
- Magee-Womens Research Institute, Department of Obstetrics, Gynecology & Reproductive Sciences, University of Pittsburgh, Pittsburgh, PA, USA
| | - Diana J Laird
- Department of Obstetrics, Gynecology & Reproductive Sciences, University of California San Francisco, San Francisco, CA, USA
| | - Paula E Cohen
- Center for Reproductive Genomics, Department of Biomedical Sciences, Cornell University, Ithaca, NY, USA
| | - Michael D Wilson
- Program in Genetics and Genome Biology, The Hospital for Sick Children, Toronto, ON, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, ON, Canada
| | - Melissa M Holmes
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON, Canada
- Department of Psychology, University of Toronto, Mississauga, Mississauga, ON, Canada
| | - Ned J Place
- Department of Population Medicine & Diagnostic Sciences, Cornell University, Ithaca, NY, USA.
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6
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Oka K, Yamakawa M, Kawamura Y, Kutsukake N, Miura K. The Naked Mole-Rat as a Model for Healthy Aging. Annu Rev Anim Biosci 2023; 11:207-226. [PMID: 36318672 DOI: 10.1146/annurev-animal-050322-074744] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Naked mole-rats (NMRs, Heterocephalus glaber) are the longest-lived rodents with a maximum life span exceeding 37 years. They exhibit a delayed aging phenotype and resistance to age-related functional decline/diseases. Specifically, they do not display increased mortality with age, maintain several physiological functions until nearly the end of their lifetime, and rarely develop cancer and Alzheimer's disease. NMRs live in a hypoxic environment in underground colonies in East Africa and are highly tolerant of hypoxia. These unique characteristics of NMRs have attracted considerable interest from zoological and biomedical researchers. This review summarizes previous studies of the ecology, hypoxia tolerance, longevity/delayed aging, and cancer resistance of NMRs and discusses possible mechanisms contributing to their healthy aging. In addition, we discuss current issues and future perspectives to fully elucidate the mechanisms underlying delayed aging and resistance to age-related diseases in NMRs.
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Affiliation(s)
- Kaori Oka
- Department of Aging and Longevity Research, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan; , ,
| | - Masanori Yamakawa
- Department of Evolutionary Studies of Biosystems, Sokendai (The Graduate University for Advanced Studies), Kanagawa, Japan; ,
| | - Yoshimi Kawamura
- Department of Aging and Longevity Research, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan; , ,
| | - Nobuyuki Kutsukake
- Department of Evolutionary Studies of Biosystems, Sokendai (The Graduate University for Advanced Studies), Kanagawa, Japan; , .,Research Center for Integrative Evolutionary Science, Sokendai (The Graduate University for Advanced Studies), Kanagawa, Japan
| | - Kyoko Miura
- Department of Aging and Longevity Research, Faculty of Life Sciences, Kumamoto University, Kumamoto, Japan; , , .,Center for Metabolic Regulation of Healthy Aging, Kumamoto University, Kumamoto, Japan
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7
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Lee R, Chu CYC. Reproduction and production in a social context: Group size, reproductive skew and increasing returns. Ecol Lett 2023; 26:219-231. [PMID: 36604867 PMCID: PMC10107238 DOI: 10.1111/ele.14157] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Revised: 11/28/2022] [Accepted: 11/29/2022] [Indexed: 01/07/2023]
Abstract
Evolutionary success requires both production (acquisition of food, protection and warmth) and reproduction. We suggest that both may increase disproportionately as group size grows, reflecting 'increasing returns' or 'group augmentation benefits', raising fitness in groups that cooperate in production and limit reproduction to one or a few high fertility females supported by non-reproductives, with high reproductive skew. In our optimisation theory both Allee effects (when individual fitness increases with group size or density) and reproductive skew arise when increasing returns determine optimal group size and proportion of reproductive females. Depending on which of food or maternal time is more important for reproduction, evolutionary trajectories of lineages may (1) reach a boundary constraint where only one female reproduces in a period (as with African wild dogs) or (2) reach a boundary where all females reproduce during their lifetimes but only during an early life stage (human menopause) or a late life stage (birds with non-dispersing helpers), where stage length optimises the proportion of females that is reproductive at any time or (3) reach the intersection of these boundary constraints where a single reproductive female is fully specialised in reproduction (as with eusocial insects). We end with some testable hypotheses.
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Affiliation(s)
- Ronald Lee
- Graduate School in Demography and Economics, Berkeley, California, USA
| | - C Y Cyrus Chu
- Graduate School in Demography and Economics, Berkeley, California, USA
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8
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Ragland NH, Compo NR, Wiltshire N, Shepard A, Troutman S, Kissil JL, Engelman RW. Housing and Husbandry Alternatives for Naked Mole Rat Colonies Used in Research Settings. JOURNAL OF THE AMERICAN ASSOCIATION FOR LABORATORY ANIMAL SCIENCE : JAALAS 2022; 61:412-418. [PMID: 35944976 PMCID: PMC9536831 DOI: 10.30802/aalas-jaalas-22-000035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Naked mole rats (Heterocephalus glaber) are a unique rodent species originating in Africa and are increasingly being used in research. Their needs and characteristics differ from those of other rodents used in research. Unique housing systems are necessary to address the special macro- and microenvironmental requirements of NMRs. Naked mole rats are one of the 2 known eusocial mammalian species, are extremely long-living, are active burrowers, and are accustomed to a subterranean environment. Unlike typical rats and mice, naked mole rats need specific, unique housing systems that mimic their natural subterranean environment to support health and longevity. Here we provide an overview of naked mole rats and a housing method that can be used in research settings.
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Affiliation(s)
- Natalie H Ragland
- Department of Biomedical Sciences, Ross University School of Veterinary Medicine, Basseterre, Saint Kitts and Nevis,Corresponding author.
| | - Nicole R Compo
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Norman Wiltshire
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Alyssa Shepard
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Scott Troutman
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Joseph L Kissil
- H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
| | - Robert W Engelman
- Department of Comparative Medicine, University of South Florida, Tampa, Florida,,H. Lee Moffitt Cancer Center & Research Institute, Tampa, Florida
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9
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Zöttl M, Bensch HM, Finn KT, Hart DW, Thorley J, Bennett NC, Braude S. Capture Order Across Social Bathyergids Indicates Similarities in Division of Labour and Spatial Organisation. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.877221] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The social mole-rats of the family Bathyergidae show elaborate social organisation that may include division of labour between breeders and non-breeders as well as across non-breeders within their groups. However, comparative behavioural data across the taxa are rare and contrasts and similarities between species are poorly understood. Field studies of social bathyergids usually involve capturing all group members until the entire group is captured. Because each animal is only captured once and traps are typically placed in close proximity to active foraging areas, the order in which animals are captured provides an indication of the foraging activity of different individuals and of the spatial organisation of the group within the burrow system. Here, we compare the association of capture order with breeding status, sex, and body mass in four species and subspecies of social bathyergids, which vary in group size and represent all three social genera within the family Bathyergidae. We show that in naked and Damaraland mole-rats (Heterocephalus glaber and Fukomys damarensis), male and female breeders are captured later than non-breeders, whereas in two different subspecies of the genus Cryptomys only female breeders are captured later than non-breeders. The effect sizes vary largely and are 10 times larger in naked mole-rats as compared to Fukomys and 3–4 times larger than in Cryptomys. Among non-breeders, sex effects are notably absent in all species and body mass predicted capture order in both naked and Damaraland mole-rats. In naked mole-rats, larger non-breeders were captured earlier than smaller ones, whereas in Damaraland mole-rats intermediate-sized non-breeders were captured first. Our data suggest that there are similarities in behavioural structure and spatial organisation across all social bathyergid species, though the most pronounced differences within groups are found in naked mole-rats.
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10
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Hite NJ, Sudheimer KD, Anderson L, Sarko DK. Spatial Learning and Memory in the Naked Mole-Rat: Evolutionary Adaptations to a Subterranean Niche. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.879989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Evolutionary adaptation to a subterranean habitat consisting of extensive underground tunnel systems would presumably require adept spatial learning and memory, however, such capabilities have not been characterized to date in naked mole-rats (Heterocephalus glaber) which, like other members of Bathyergidae, are subterranean rodents. The goal of this study was to develop a method for effectively assessing spatial learning and memory by modifying a Hebb-Williams maze for use with these subterranean rodents. Established behavioral tests to assess spatial learning and memory have primarily focused on, and have been optimized for, more typical laboratory rodent species such as mice and rats. In the current study, we utilized species-appropriate motivators, analyzed learning curves associated with maze performance, and tested memory retention in naked mole-rats. Using a modified Hebb-Williams maze, naked mole-rats underwent 3 days of training, consisting of five trials per day wherein they could freely explore the maze in search of the reward chamber. Memory retention was then tested 1 day, 1 week, and 1 month following the last day of training. Performance was analyzed based on latency to the reward chamber, errors made, and distance traveled to reach the reward chamber. Overall, this study established a behavioral paradigm for assessing maze navigation, spatial learning, and spatial memory in subterranean rodents, including optimization of rewards and environmental motivators.
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11
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Lutermann H. Socializing in an Infectious World: The Role of Parasites in Social Evolution of a Unique Rodent Family. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.879031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Transmission of parasites between hosts is facilitated by close contact of hosts. Consequently, parasites have been proposed as an important constraint to the evolution of sociality accounting for its rarity. Despite the presumed costs associated with parasitism, the majority of species of African mole-rats (Family: Bathyergidae) are social. In fact, only the extremes of sociality (i.e., solitary and singular breeding) are represented in this subterranean rodent family. But how did bathyergids overcome the costs of parasitism? Parasite burden is a function of the exposure and susceptibility of a host to parasites. In this review I explore how living in sealed burrow systems and the group defenses that can be employed by closely related group members can effectively reduce the exposure and susceptibility of social bathyergids to parasites. Evidence suggests that this can be achieved largely by investment in relatively cheap and flexible behavioral rather than physiological defense mechanisms. This also shifts the selection pressure for parasites on successful transmission between group members rather than transmission between groups. In turn, this constrains the evolution of virulence and favors socially transmitted parasites (e.g., mites and lice) further reducing the costs of parasitism for social Bathyergidae. I conclude by highlighting directions for future research to evaluate the mechanisms proposed and to consider parasites as facilitators of social evolution not only in this rodent family but also other singular breeders.
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12
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Szafranski K, Wetzel M, Holtze S, Büntjen I, Lieckfeldt D, Ludwig A, Huse K, Platzer M, Hildebrandt T. The Mating Pattern of Captive Naked Mole-Rats Is Best Described by a Monogamy Model. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.855688] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Naked mole-rats form colonies with a single reproductively active female surrounded by subordinate workers. Workers perform offspring care, construction and defense of the burrow system, and food supply. Such division of labor, called “cooperative breeding,” is strongly associated with the evolution of monogamous mating behavior, as seen in several mammalian lineages. This association is explained by the evolutionary theory of kin selection, according to which a subordinate adult may help to raise other’s offspring if they are in full sibling relationship. In conflict with this theory, the naked mole-rat is widely considered to be polyandrous, based on reports on multiple males contributing to a colony’s progeny. In order to resolve this contrast, we undertook an in-depth microsatellite-based kinship analysis on captive colonies. Four independent colonies comprising a total of 265 animals were genotyped using a panel of 73 newly established microsatellite markers. Our results show that each mole-rat colony contains a single monogamous breeder pair, which translates to a reproductive skew of 100% for both sexes. This finding, also in conjunction with previously published parental data, favors monogamy as the best-fitting model to describe naked mole-rat reproduction patterns. Polyandry or other polygamous reproduction models are disfavored and should be considered as exceptional. Overall, the empirical genetic data are in agreement with the kin selection theory.
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13
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Toor I, Maynard R, Peng X, Beery AK, Holmes MM. Naked Mole-Rat Social Phenotypes Vary in Investigative and Aggressive Behavior in a Laboratory Partner Preference Paradigm. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.860885] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Here we employed the partner preference test (PPT) to examine how naked mole-rat non-breeding individuals of different behavioral phenotypes make social decisions. Naked mole-rats from six colonies were classified into three behavioral phenotypes (soldiers, dispersers, and workers) using a battery of behavioral tests. They then participated in a 3 h long PPT, where they could freely interact with a tethered familiar or tethered unfamiliar conspecific. By comparing the three behavioral phenotypes, we tested the hypothesis that the PPT can be used to interrogate social decision-making in this species, revealing individual differences in behavior that are consistent with discrete social phenotypes. We also tested whether a shorter, 10 min version of the paradigm is sufficient to capture group differences in behavior. Overall, soldiers had higher aggression scores toward unfamiliar conspecifics than both workers and dispersers at the 10 min and 3 h comparison times. At the 10 min comparison time, workers showed a stronger preference for the familiar animal’s chamber, as well as for investigating the familiar conspecific, compared to both dispersers and soldiers. At the 3 h time point, no phenotype differences were seen with chamber or investigation preference scores. Overall, all phenotypes spent more time in chambers with another animal vs. being alone. Use of the PPT in a comparative context has demonstrated that the test identifies species and group differences in affiliative and aggressive behavior toward familiar and unfamiliar animals, revealing individual differences in social decision-making and, importantly, capturing aspects of species-specific social organization seen in nature.
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