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Taraporevala NF, Lesoway MP, Goodheart JA, Lyons DC. Precocious Sperm Exchange in the Simultaneously Hermaphroditic Nudibranch, Berghia stephanieae. Integr Org Biol 2022; 4:obac030. [PMID: 36089995 PMCID: PMC9449679 DOI: 10.1093/iob/obac034] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2022] [Revised: 06/10/2022] [Accepted: 07/28/2022] [Indexed: 11/15/2022] Open
Abstract
Sexual systems vary greatly across molluscs. This diversity includes simultaneous hermaphroditism, with both sexes functional at the same time. Most nudibranch molluscs are thought to be simultaneous hermaphrodites, but detailed studies of reproductive development and timing remain rare as most species cannot be cultured in the lab. The aeolid nudibranch, Berghia stephanieae, is one such species that can be cultured through multiple generations on the benchtop. We studied B. stephanieae reproductive timing to establish when animals first exchange sperm and how long sperm can be stored. We isolated age- and size-matched individuals at sequential timepoints to learn how early individuals can exchange sperm. Individuals isolated at 10 weeks post initial feeding (wpf; ∼13 weeks postlaying [wpl]) can produce fertilized eggs. This is 6 weeks before animals first lay egg masses, indicating that sperm exchange occurs well before individuals are capable of laying eggs. Our results indicate that male gonads become functional for animals between 6 mm (∼6 wpf, ∼9 wpl) and 9 mm (∼12 wpf, ∼15 wpl) in length. That is much smaller (and sooner) than the size (and age) of individuals at first laying (12–19 mm; ∼16 wpf, ∼19 wpl), indicating that male and female functions do not develop simultaneously. We also tracked the number of fertilized eggs in each egg mass, which remained steady for the first 10–15 egg masses, followed by a decline to near-to-no fertilization. This dataset provides insights into the precise timing of the onset of functionality of the male and female reproductive systems in B. stephanieae. These data contribute to a broader understanding of reproductive development and the potential for understanding the evolution of diverse sexual systems in molluscs.
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Affiliation(s)
- Neville F Taraporevala
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Maryna P Lesoway
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Jessica A Goodheart
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Deirdre C Lyons
- Scripps Institution of Oceanography, University of California San Diego , 9500 Gilman Drive, La Jolla, CA 92093, USA
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Lorenzi MC, Araguas A, Bocquet C, Picchi L, Ricci-Bonot C. Courtship behavior as a war of attrition in a simultaneous hermaphrodite. ANIM BIOL 2019. [DOI: 10.1163/15707563-00001050] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Abstract
In outcrossing hermaphrodites with unilateral mating, where for each mating interaction one individual assumes the female role and the other the male role, each individual must take a sexual role opposite to that of its partner. In the polychaete worm Ophryotrocha diadema, the decision on sexual role is likely at stake during the day-long courtship. Here we describe, for the first time, courtship and pseudocopulation in this species, quantify their pre-copulatory behavior, and search for behavioral traits predicting the prospective sexual role (i.e., behavioral sexual dimorphism), by analyzing the courtship behavior of pairs of worms during the day preceding a mating event. We did not find any behavioral cue predicting the sexual role worms were to play; partners’ pre-copulatory behaviors were qualitatively and quantitatively symmetrical. We interpret this as the outcome of a war of attrition where partners share the preference for the same sexual role, and both hide their ‘willingness’ to play the less preferred one, until one individual reaches its cost threshold and accepts the less preferred sexual role.
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Affiliation(s)
- Maria Cristina Lorenzi
- LEEC – Laboratoire d’Ethologie Expérimentale et Comparée, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France
| | - Alice Araguas
- LEEC – Laboratoire d’Ethologie Expérimentale et Comparée, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France
| | - Céline Bocquet
- LEEC – Laboratoire d’Ethologie Expérimentale et Comparée, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France
| | - Laura Picchi
- LEEC – Laboratoire d’Ethologie Expérimentale et Comparée, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France
| | - Claire Ricci-Bonot
- LEEC – Laboratoire d’Ethologie Expérimentale et Comparée, Université Paris 13, Sorbonne Paris Cité, 99 avenue J.-B. Clément, 93430 Villetaneuse, France
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Bonel N, Noël E, Janicke T, Sartori K, Chapuis E, Ségard A, Meconcelli S, Pélissié B, Sarda V, David P. Asymmetric evolutionary responses to sex-specific selection in a hermaphrodite. Evolution 2018; 72:2181-2201. [PMID: 30109706 DOI: 10.1111/evo.13565] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2018] [Accepted: 07/25/2018] [Indexed: 01/10/2023]
Abstract
Sex allocation theory predicts that simultaneous hermaphrodites evolve to an evolutionary stable resource allocation, whereby any increase in investment to male reproduction leads to a disproportionate cost on female reproduction and vice versa. However, empirical evidence for sexual trade-offs in hermaphroditic animals is still limited. Here, we tested how male and female reproductive traits evolved under conditions of reduced selection on either male or female reproduction for 40 generations in a hermaphroditic snail. This selection favors a reinvestment of resources from the sex function under relaxed selection toward the other function. We found no such evolutionary response. Instead, juvenile survival and male reproductive success significantly decreased in lines where selection on the male function (i.e., sexual selection) was relaxed, while relaxing selection on the female function had no effect. Our results suggest that most polymorphisms under selection in these lines were not sex-antagonistic. Rather, they were deleterious mutations affecting juvenile survival (thus reducing both male and female fitness) with strong pleiotropic effects on male success in a sexual selection context. These mutations accumulated when sexual selection was relaxed, which supports the idea that sexual selection in hermaphrodites contributes to purge the mutation load from the genome as in separate-sex organisms.
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Affiliation(s)
- Nicolás Bonel
- Laboratorio de Zoología de Invertebrados I, Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, San Juan 670, B8000ICN, Bahía Blanca, CONICET, Argentina.,Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
| | - Elsa Noël
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France.,Institute for Population Genetics, University of Veterinary Medicine, Veterinärplatz 1, A-1210, Vienna, Austria
| | - Tim Janicke
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France.,School of Life Sciences, University of Sussex, Falmer, Brighton, BN1 9QG, United Kingdom
| | - Kevin Sartori
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
| | - Elodie Chapuis
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France.,IRD, UMR186 Intéractions Plantes-Microrganismes-Environement, 911, Avenue Agropolis, BP 64501 34394 Montpellier Cedex 05, France.,CIRAD, UMR PVBMT, F-97410 St Pierre, La Réunion, France
| | - Adeline Ségard
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
| | - Stefania Meconcelli
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France.,Department of Life Sciences and Systems Biology, Università di Torino, Turin, Italy
| | - Benjamin Pélissié
- University of Wisconsin Madison, Department of Entomology, 1630 Linden Dr, Madison, Wisconsin 53706
| | - Violette Sarda
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
| | - Patrice David
- Centre d'Ecologie Fonctionnelle et Evolutive, UMR 5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, Ecole Pratique des Hautes Etudes, 1919 Route de Mende, 34293 Montpellier Cedex 05, France
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Bürkli A, Jokela J. Increase in multiple paternity across the reproductive lifespan in a sperm-storing, hermaphroditic freshwater snail. Mol Ecol 2017; 26:5264-5278. [PMID: 28605149 DOI: 10.1111/mec.14200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2016] [Revised: 06/01/2017] [Accepted: 06/02/2017] [Indexed: 12/28/2022]
Abstract
Polyandry is a common phenomenon and challenges the traditional view of stronger sexual selection in males than in females. In simultaneous hermaphrodites, the physical proximity of both sex functions was long thought to preclude the operation of sexual selection. Laboratory studies suggest that multiple mating and polyandry in hermaphrodites may actually be common, but data from natural populations are sparse. We therefore estimated the rate of multiple paternity and its seasonal variability in the annual, sperm-storing, simultaneously hermaphroditic freshwater snail Radix balthica for the entire duration of the reproductive lifespan. We also tested whether multiple paternity was associated with clutch size or embryonic development. To obtain these data, we measured and genotyped 60 field-collected egg clutches using nine highly polymorphic microsatellite markers. Overall, 50% of the clutches had multiple fathers, and both the frequency (20-93% of clutches) and magnitude of multiple paternity (mean 1.3-3.8 fathers per clutch) substantially increased over time, probably because of extensive sperm storage. Most multiply sired clutches (83%) had a dominant father, but neither clutch size nor the proportion of developed embryos per clutch was associated with levels of multiple paternity. Both the evident promiscuity and the frequent skew of paternity shares suggest that sexual selection may be an important evolutionary force in the study population.
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Affiliation(s)
- Anja Bürkli
- Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.,ETH Zurich, D-USYS, Institute of Integrative Biology, Zürich, Switzerland
| | - Jukka Jokela
- Department of Aquatic Ecology, EAWAG, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.,ETH Zurich, D-USYS, Institute of Integrative Biology, Zürich, Switzerland
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6
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David KT, Tanabe P, Fieber LA. Resource Availability Drives Mating Role Selection in a Simultaneous Hermaphrodite Aplysia californica. THE BIOLOGICAL BULLETIN 2016; 231:199-206. [PMID: 28048961 PMCID: PMC5365073 DOI: 10.1086/691067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
In simultaneous hermaphrodites, a clear conflict exists between sperm donor and sperm recipient roles, and how such conflict is mediated remains up for debate. This study observed and recorded mating role selection as a function of resource availability in the simultaneous hermaphrodite Aplysia californica. When food was plentiful, animals assumed both sperm donor and recipient roles at relatively even frequency. However, when half of the mating pairs were placed on restricted diets, food-limited animals assumed the sperm donor role at significantly (P < 0.05) greater frequency than their ad libitum partners; nevertheless, the frequency of successful mating events remained the same. The mass and frequency of eggs laid were also significantly (P > 0.05) correlated with parental food intake. These results demonstrate how mating strategies can change within a mating season, as a result of shifting environmental conditions, and call for a diverse framework to address these issues in simultaneous hermaphroditic mating systems.
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7
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Graham S, Chapuis E, Meconcelli S, Bonel N, Sartori K, Christophe A, Alda P, David P, Janicke T. Size-assortative mating in simultaneous hermaphrodites: an experimental test and a meta-analysis. Behav Ecol Sociobiol 2015. [DOI: 10.1007/s00265-015-1999-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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8
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Nakadera Y, Swart EM, Maas JPA, Montagne-Wajer K, Ter Maat A, Koene JM. Effects of age, size, and mating history on sex role decision of a simultaneous hermaphrodite. ACTA ACUST UNITED AC 2014; 26:232-241. [PMID: 25713474 PMCID: PMC4309981 DOI: 10.1093/beheco/aru184] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2014] [Revised: 09/12/2014] [Accepted: 09/16/2014] [Indexed: 11/13/2022]
Abstract
Quite a few animals are male and female at the same time, so they can choose to mate either as male or female on copulation. The decision to perform either sex role was known to be highly flexible depending on various, but often confounding, factors. For the pond snail, we report that young and small snails tend to mate as males first, though old and large snails do not seem to be better females. Contrasting with separate-sexed animals, simultaneous hermaphrodites display unique reproductive strategies as they are male and female at the same time. Simultaneous hermaphrodites that copulate unilaterally, for instance, make a decision to mate as a male or female. Previous studies have demonstrated that sex role preference in hermaphrodites is flexible and is controlled by several, often confounding, factors. We examined the relationship between sex role decisions and 3 life-history traits (age, size, and mating history) in the great pond snail, Lymnaea stagnalis. Based on our field observations, which indicate that adult individuals show overlapping generations and large variation in body size during the breeding season, we performed a sex role choice experiment in the laboratory. We found that young and small snails mate as males first. Both age and size significantly affected sex role decision, with age having a stronger effect. Furthermore, we tested whether L. stagnalis becomes reluctant to inseminate a mate after being inseminated because it is known that after insemination, male investment substantially reduces. Contrary to expectations, our results indicate that the receipt of seminal fluid does not seem to reduce male motivation. In sum, sex role decisions in L. stagnalis are largely determined by age and size but not by having received seminal fluid. This mating pattern, however, does not fully support the size-advantage model because large or old individuals did not perform better as females in our experiment. These results imply a conflicting mating interest, rather than harmonious agreement, between age- and size-different hermaphrodites.
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Affiliation(s)
- Yumi Nakadera
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam , De Boelelaan 1085, 1081HV Amsterdam , The Netherlands
| | - Elferra M Swart
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam , De Boelelaan 1085, 1081HV Amsterdam , The Netherlands
| | - Jeroen P A Maas
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam , De Boelelaan 1085, 1081HV Amsterdam , The Netherlands , ; Applied Biology, HAS University of Applied Sciences , Onderwijsboulevard 221, 5223DE 's-Hertogenbosch , The Netherlands , and
| | - Kora Montagne-Wajer
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam , De Boelelaan 1085, 1081HV Amsterdam , The Netherlands
| | - Andries Ter Maat
- Behavioural Neurobiology, Max Planck Institute for Ornithology , Eberhard-Gwinner-Strasse, 82319 Seewiesen , Germany
| | - Joris M Koene
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam , De Boelelaan 1085, 1081HV Amsterdam , The Netherlands
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9
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Anthes N, Werminghausen J, Lange R. Large donors transfer more sperm, but depletion is faster in a promiscuous hermaphrodite. Behav Ecol Sociobiol 2013. [DOI: 10.1007/s00265-013-1662-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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Kimura K, Chiba S. Strategic ejaculation in simultaneously hermaphroditic land snails: more sperm into virgin mates. BMC Evol Biol 2013; 13:264. [PMID: 24304518 PMCID: PMC4235035 DOI: 10.1186/1471-2148-13-264] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2013] [Accepted: 11/27/2013] [Indexed: 11/15/2022] Open
Abstract
Background It has been theorised that sperm competition promotes the strategic usage of costly sperm. Although sperm competition is thought to be an important driving force of reproductive traits in simultaneous hermaphrodites as well as in species with separate sexes, empirical studies on strategic ejaculation in simultaneous hermaphrodites are scarce. Results In the present study, we tested whether the simultaneously hermaphroditic land snail Euhadra quaesita adjusts the number of sperm donated according to the condition of the mate and whether the pattern of strategic ejaculation is in line with previously suggested theories. We found that individuals donated much more sperm when they copulated with a virgin mate than when they copulated with a non-virgin. Conclusion The virgin-biased pattern of ejaculation matches the theoretical prediction and suggests that sperm competition significantly influence the reproductive traits of simultaneously hermaphroditic land snails.
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Affiliation(s)
- Kazuki Kimura
- Department of Environmental Life Sciences, Graduate School of Life Sciences, Tohoku University, Kawauchi 41, Aoba-ku, Sendai 980-8576, Japan.
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Lorenzi MC, Schleicherová D, Sella G. Multiple paternity and mate competition in non-selfing, monogamous, egg-trading hermaphrodites. Acta Ethol 2013. [DOI: 10.1007/s10211-013-0169-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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12
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Yu TL, Wang LM. Mate Choice and Mechanical Constraint on Size-Assortative Paring Success in a Simultaneous Hermaphroditic Pond SnailRadix lagotis(Gastropoda: Pulmonata) on the Tibetan Plateau. Ethology 2013. [DOI: 10.1111/eth.12114] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Tong Lei Yu
- Department of Zoology; College of Life Science; Xinyang Normal University; Xinyang China
| | - Li Ming Wang
- Department of Zoology; College of Life Science; Xinyang Normal University; Xinyang China
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13
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Nakadera Y, Koene JM. Reproductive strategies in hermaphroditic gastropods: conceptual and empirical approaches. CAN J ZOOL 2013. [DOI: 10.1139/cjz-2012-0272] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
An individual optimizes its reproductive success by adopting a particular reproductive strategy. Studying the details of a reproductive strategy leads to an understanding of how sexual selection acts, as the former is the process via which the individual reproduces successfully. Hermaphroditic gastropods display a bewildering diversity of reproductive strategies, which may be due to their mode of gender expression, when compared with well-studied separate-sexed species. Extensive theoretical, observational, and experimental research has been conducted on this topic. However, despite our knowledge about the reproductive system of hermaphroditic gastropods, we still need to fill the gap between pre- and post-copulatory processes and reproductive success. Here, we review and propose conceptual and empirical approaches aimed at understanding reproductive strategies of hermaphroditic gastropods. In sum, our suggestions are (i) to focus on sex-biased traits, (ii) to take biologically reliable measurements at both the pre- and post-copulatory level that relate to reproductive success, and (iii) to examine the fitness consequences of biased sex allocation.
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Affiliation(s)
- Yumi Nakadera
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081HV, Amsterdam, the Netherlands
| | - Joris M. Koene
- Section Animal Ecology, Department of Ecological Science, Faculty of Earth and Life Sciences, VU University Amsterdam, De Boelelaan 1085, 1081HV, Amsterdam, the Netherlands
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14
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Lange R, Werminghausen J, Anthes N. Does traumatic secretion transfer manipulate mating roles or reproductive output in a hermaphroditic sea slug? Behav Ecol Sociobiol 2013. [DOI: 10.1007/s00265-013-1551-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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15
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Werminghausen J, Lange R, Anthes N. Seeking a Sex-Specific Coolidge Effect in a Simultaneous Hermaphrodite. Ethology 2013. [DOI: 10.1111/eth.12093] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Johanna Werminghausen
- Animal Evolutionary Ecology Group; Institute of Evolution and Ecology; Eberhard Karls Universität Tübingen; Tübingen; Germany
| | - Rolanda Lange
- Animal Evolutionary Ecology Group; Institute of Evolution and Ecology; Eberhard Karls Universität Tübingen; Tübingen; Germany
| | - Nils Anthes
- Animal Evolutionary Ecology Group; Institute of Evolution and Ecology; Eberhard Karls Universität Tübingen; Tübingen; Germany
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Schärer L, Pen I. Sex allocation and investment into pre- and post-copulatory traits in simultaneous hermaphrodites: the role of polyandry and local sperm competition. Philos Trans R Soc Lond B Biol Sci 2013; 368:20120052. [PMID: 23339243 PMCID: PMC3576586 DOI: 10.1098/rstb.2012.0052] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sex allocation theory predicts the optimal allocation to male and female reproduction in sexual organisms. In animals, most work on sex allocation has focused on species with separate sexes and our understanding of simultaneous hermaphrodites is patchier. Recent theory predicts that sex allocation in simultaneous hermaphrodites should strongly be affected by post-copulatory sexual selection, while the role of pre-copulatory sexual selection is much less clear. Here, we review sex allocation and sexual selection theory for simultaneous hermaphrodites, and identify several strong and potentially unwarranted assumptions. We then present a model that treats allocation to sexually selected traits as components of sex allocation and explore patterns of allocation when some of these assumptions are relaxed. For example, when investment into a male sexually selected trait leads to skews in sperm competition, causing local sperm competition, this is expected to lead to a reduced allocation to sperm production. We conclude that understanding the evolution of sex allocation in simultaneous hermaphrodites requires detailed knowledge of the different sexual selection processes and their relative importance. However, little is currently known quantitatively about sexual selection in simultaneous hermaphrodites, about what the underlying traits are, and about what drives and constrains their evolution. Future work should therefore aim at quantifying sexual selection and identifying the underlying traits along the pre- to post-copulatory axis.
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Affiliation(s)
- Lukas Schärer
- Evolutionary Biology, Zoological Institute, University of Basel, Vesalgasse 1, 4051 Basel, Switzerland.
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Sprenger D, Lange R, Anthes N. Population density and group size effects on reproductive behavior in a simultaneous hermaphrodite. BMC Evol Biol 2011; 11:107. [PMID: 21501499 PMCID: PMC3090356 DOI: 10.1186/1471-2148-11-107] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Accepted: 04/18/2011] [Indexed: 11/29/2022] Open
Abstract
Background Despite growing evidence that population dynamic processes can have substantial effects on mating system evolution, little is known about their effect on mating rates in simultaneous hermaphrodites. According to theory, mating rate is expected to increase with mate availability because mating activity is primarily controlled by the male sexual function. A different scenario appears plausible in the hermaphroditic opisthobranch Chelidonura sandrana. Here, field mating rates are close to the female fitness optimum, suggesting that mating activity remains unresponsive to variation in mate availability. Results Applying an experimental design that aims at independent experimental manipulation of density and social group size, we find substantial increases in mate encounter rate with both factors, but no statistically detectable effects on mating rate in C. sandrana. Instead, mating rate remained close to the earlier determined female fitness optimum. Conclusions We demonstrate that mating rate in C. sandrana is largely unresponsive to variation in mate availability and is maintained close to the female fitness optimum. These findings challenge the prevailing notion of male driven mating rates in simultaneous hermaphrodites and call for complementary investigations of mating rate effects on fitness through the male sexual function.
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Affiliation(s)
- Dennis Sprenger
- Animal Evolutionary Ecology, Institute of Evolution and Ecology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
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Kelly CD, Jennions MD. Sexual selection and sperm quantity: meta-analyses of strategic ejaculation. Biol Rev Camb Philos Soc 2011; 86:863-84. [PMID: 21414127 DOI: 10.1111/j.1469-185x.2011.00175.x] [Citation(s) in RCA: 214] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Clint D Kelly
- Department of Ecology, Evolution & Organismal Biology, Iowa State University, Ames, USA.
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Effects of body size on courtship role, mating frequency and sperm transfer in the land snail Succinea putris. Anim Behav 2010. [DOI: 10.1016/j.anbehav.2010.02.010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Sandner P, Schärer L. No Plastic Responses to Experimental Manipulation of Sperm Competitionper sein a Free-Living Flatworm. Ethology 2010. [DOI: 10.1111/j.1439-0310.2010.01746.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Benke M, Reise H, Montagne-Wajer K, Koene JM. Cutaneous application of an accessory-gland secretion after sperm exchange in a terrestrial slug (Mollusca: Pulmonata). ZOOLOGY 2010; 113:118-24. [PMID: 20202803 DOI: 10.1016/j.zool.2009.08.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Revised: 07/30/2009] [Accepted: 08/21/2009] [Indexed: 10/19/2022]
Abstract
Competition for fertilisation in hermaphroditic animals seems to have led to many odd behaviours and complex morphologies involved in the transfer of accessory-gland products to the partner. Terrestrial slugs of the genus Deroceras show remarkably elaborate and interspecifically diverse penis morphologies and mating behaviours. Most species have an appending penial gland, which in Deroceras panormitanum consists of a few long fingers that are everted after sperm exchange and laid onto the partner's back. To investigate whether this gland transfers a secretion onto the partner's skin, we killed slugs at different mating stages and studied their penial glands and skin histologically. Two types of secretion granules appeared at a very early stage of courtship, and the penial gland was already filled 15min into the courtship. At copulation, the gland everted this secretion onto the partner's body, where it remained for at least 50min. No lysis of skin tissue or other effects on the skin were observed. The slugs tried to lick the received secretion off their own body, and some droplets were observed to be shed with the body mucus. Our results indicate the external application of a glandular substance that could function as either a pheromone or allohormone. The behaviours of the recipients suggest sexual conflict, although mutual interest cannot be ruled out.
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Affiliation(s)
- Mandy Benke
- Senckenberg Museum of Natural History Görlitz, Am Museum 1, D-02826 Görlitz, Germany
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Häderer IK, Werminghausen J, Michiels NK, Timmermeyer N, Anthes N. No effect of mate novelty on sexual motivation in the freshwater snail Biomphalaria glabrata. Front Zool 2009; 6:23. [PMID: 19818155 PMCID: PMC2766376 DOI: 10.1186/1742-9994-6-23] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Accepted: 10/12/2009] [Indexed: 11/24/2022] Open
Abstract
Background When mating effort (e.g. via ejaculates) is high, males are expected to strategically allocate their resources depending on the expected fitness gains from a given mating opportunity. One mechanism to achieve strategic mating is the Coolidge effect, where male sexual motivation declines across repeated encounters with a familiar partner, but resuscitates when encountering a novel female. Experimental tests of male mate choice via mechanisms such as the Coolidge effect, however, remain scarce. Moreover, it is untested to date whether the Coolidge effect occurs in a sex-specific manner in simultaneous hermaphrodites, where the motivation to mate with a familiar partner may vary with previous mating activity in the male or female role. Results We exposed focal hermaphroditic freshwater snails, Biomphalaria glabrata, repeatedly to either a familiar or a novel partner. None of our proxies of sexual motivation (remating likelihood, mating delay, copulation duration) varied between the novel and familiar partner treatments. Moreover, the mating role taken during the first copulation did not affect the subsequent choice of mating roles in the familiar partner treatment as would be expected if focals preferred to avoid mating twice in the same role with a familiar partner. This indicates the absence of sex-specific effects of partner novelty. Conclusion Our data indicate that mate novelty does affect neither overall sexual motivation nor the choice of mating roles in B. glabrata. Hence, male mate choice via a Coolidge effect appears inexistent in this invertebrate hermaphrodite. We discuss the possible roles of insufficient fitness gains for discriminatory behaviour in populations with frequent mate encounters as well as poor mate discrimination capacities. Our findings lend also no support to the novel prediction that sexual motivation in simultaneous hermaphrodites varies with the mating roles taken during previous copulations, calling for empirical investigation in further hermaphrodite systems.
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Affiliation(s)
- Ines K Häderer
- Animal Evolutionary Ecology, Institute for Evolution and Ecology, Eberhard Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
| | - Johanna Werminghausen
- Animal Evolutionary Ecology, Institute for Evolution and Ecology, Eberhard Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
| | - Nico K Michiels
- Animal Evolutionary Ecology, Institute for Evolution and Ecology, Eberhard Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
| | - Nadine Timmermeyer
- Animal Evolutionary Ecology, Institute for Evolution and Ecology, Eberhard Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
| | - Nils Anthes
- Animal Evolutionary Ecology, Institute for Evolution and Ecology, Eberhard Karls-Universität Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany
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Smolensky N, Romero MR, Krug PJ. Evidence for costs of mating and self-fertilization in a simultaneous hermaphrodite with hypodermic insemination, the Opisthobranch Alderia willowi. THE BIOLOGICAL BULLETIN 2009; 216:188-199. [PMID: 19366929 DOI: 10.1086/bblv216n2p188] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
Simultaneous hermaphrodites offer the chance to study antagonistic coevolution between the sexes when individuals function in both roles. Traumatic mating by hypodermic insemination has repeatedly evolved in hermaphroditic taxa, but evidence for the fitness costs of such male-advantage traits is lacking. When reared in isolation, specimens of the sea slug Alderia willowi (Opisthobranchia: Sacoglossa) initially laid clutches of unfertilized eggs but 4 days later began self-fertilizing; this is only the third report of selfing in an opisthobranch. Hypodermic insemination may allow selfing in Alderia if penetration of the body wall bypasses internal mechanisms that promote outcrossing. Selfing specimens and slugs reared in pairs had reduced fecundity compared to isolated slugs laying unfertilized clutches, suggesting that hypodermic insemination imposes a cost of mating. Egg production increased for field-caught slugs separated after mating compared to slugs held in pairs, a further indication that accessibility to mates imposes a fitness cost to the female function. Such antagonism can confer a competitive advantage to slugs mating in the male role but diminish reproduction in the female role among hermaphrodites capable of long-term sperm storage. Alderia willowi is also a rare case of poecilogony, with adults producing either planktotrophic or lecithotrophic larvae. Our rearing studies revealed that most slugs switched between expressed development modes at some point; such reproductive flexibility within individuals is unprecedented, even among poecilogonous species.
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Affiliation(s)
- Nicole Smolensky
- Department of Biological Sciences, California State University, Los Angeles, California 90032-8201, USA
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Sprenger D, Lange R, Michiels NK, Anthes N. The role of body size in early mating behavior in a simultaneous hermaphrodite, Chelidonura sandrana. Behav Ecol Sociobiol 2009. [DOI: 10.1007/s00265-009-0738-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Abstract
Sex allocation is a crucial life-history parameter in all sexual organisms. Over the last decades a body of evolutionary theory, sex allocation theory, was developed, which has yielded capital insight into the evolution of optimal sex allocation patterns and adaptive evolution in general. Most empirical work, however, has focused on species with separate sexes. Here I review sex allocation theory for simultaneous hermaphrodites and summarize over 50 empirical studies, which have aimed at evaluating this theory in a diversity of simultaneous hermaphrodites spanning nine animal phyla. These studies have yielded considerable qualitative support for several predictions of sex allocation theory, such as a female-biased sex allocation when the number of mates is limited, and a shift toward a more male-biased sex allocation with increasing numbers of mates. In contrast, many fundamental assumptions, such as the trade-off between male and female allocation, and numerous predictions, such as brooding limiting the returns from female allocation, are still poorly supported. Measuring sex allocation in simultaneously hermaphroditic animals remains experimentally demanding, which renders evaluation of more quantitative predictions a challenging task. I identify the main questions that need to be addressed and point to promising avenues for future research.
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Affiliation(s)
- Lukas Schärer
- University of Basel, Zoological Institute, Evolutionary Biology, Vesalgasse 1, 4051 Basel, Switzerland.
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Janicke T, Schärer L. Determinants of mating and sperm-transfer success in a simultaneous hermaphrodite. J Evol Biol 2009; 22:405-15. [PMID: 19196388 DOI: 10.1111/j.1420-9101.2008.01660.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The number of mating partners an individual has within a population is a crucial parameter in sex allocation theory for simultaneous hermaphrodites because it is predicted to be one of the main parameters influencing sex allocation. However, little is known about the factors that determine the number of mates in simultaneous hermaphrodites. Furthermore, in order to understand the benefits obtained by resource allocation into the male function it is important to identify the factors that predict sperm-transfer success, i.e. the number of sperm a donor manages to store in a mate. In this study we experimentally tested how social group size (i.e. the number of all potential mates within a population) and density affect the number of mates and sperm-transfer success in the outcrossing hermaphroditic flatworm Macrostomum lignano. In addition, we assessed whether these parameters covary with morphological traits, such as body size, testis size and genital morphology. For this we used a method, which allows tracking sperm of a labelled donor in an unlabelled mate. We found considerable variation in the number of mates and sperm-transfer success between individuals. The number of mates increased with social group size, and was higher in worms with larger testes, but there was no effect of density. Similarly, sperm-transfer success was affected by social group size and testis size, but in addition this parameter was influenced by genital morphology. Our study demonstrates for the first time that the social context and the morphology of sperm donors are important predictors of the number of mates and sperm-transfer success in a simultaneous hermaphrodite. Based on these findings, we hypothesize that sex allocation influences the mating behaviour and outcome of sperm competition.
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Affiliation(s)
- T Janicke
- Zoological Institute, University of Basel, Basel, Switzerland.
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MORITA MASAYA, SEKI SATOKO. Sperm movement and morphology in a simultaneous hermaphroditic sea slug. INVERTEBR REPROD DEV 2009. [DOI: 10.1080/07924259.2009.9652291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Norton CG, Johnson AF, Mueller RL. Relative size influences gender role in the freshwater hermaphroditic snail, Helisoma trivolvis. Behav Ecol 2008. [DOI: 10.1093/beheco/arn099] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Velando A, Eiroa J, Domínguez J. Brainless but not clueless: earthworms boost their ejaculates when they detect fecund non-virgin partners. Proc Biol Sci 2008; 275:1067-72. [PMID: 18252668 PMCID: PMC2600910 DOI: 10.1098/rspb.2007.1718] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2007] [Revised: 01/11/2008] [Accepted: 01/14/2008] [Indexed: 11/12/2022] Open
Abstract
In many animals in which females store sperm, males may detect female mating status and, in order to outcompete rival sperm, increase ejaculate size when copulating with non-virgin females. Although most studies have been restricted to organisms with separate sexes, theoretical models suggest that sperm competition should also be an important selective agent shaping life-history traits in simultaneous hermaphrodites. Nevertheless, the empirical support for ejaculate adjustment in a mating opportunity is scarce in hermaphrodites. In the present study, we performed a double-mating experiment to determine whether earthworms (Eisenia andrei) detect the mating status of their partners and whether they respond by adjusting their ejaculate. We found that earthworms triplicated the donated sperm when mating with a non-virgin mate. Moreover, such increases were greater when the worms were mated with larger (more fecund) partners, indicating that earthworms perform a fine-tune control of ejaculate volume. The results of the present study suggest that, under high intensity of sperm competition, partner evaluation is subject to intense selection in hermaphrodite animals, and donors are selective about to whom they donate how much sperm.
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Affiliation(s)
| | | | - Jorge Domínguez
- Departamento de Ecoloxía e Bioloxía Animal, Campus Lagoas-Marcosende, Universidade de Vigo36310 Vigo, Spain
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Effects of isolation and body size on the mating behaviour of the hermaphroditic land snail Succinea putris. Anim Behav 2008. [DOI: 10.1016/j.anbehav.2007.09.014] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Sprenger D, Faber J, Michiels NK, Anthes N. Natural female mating rate maximizes hatchling size in a marine invertebrate. J Anim Ecol 2008; 77:696-701. [PMID: 18298520 DOI: 10.1111/j.1365-2656.2008.01376.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1. Males and females often differ in their optimal mating rates, resulting potentially in conflicts over remating. In species with separate sexes, females typically have a lower optimal mating rate than males, and can regulate contacts with males accordingly. The realized mating rate may therefore be closer to the female's optimum. In simultaneous hermaphrodites, however, it has been suggested that the intraindividual optimization between 'male' and 'female' interests generates more 'male'-driven mating rates. 2. In order to assess the consequences of variation in mating rate on 'female' reproductive output, we exposed the simultaneously hermaphroditic sea slug Chelidonura sandrana to four mating rate regimes and recorded the effects on a variety of fitness components. 3. In focal 'females', we found (i) a slight but significant linear decrease in fecundity with mating rate, whereas (ii) maternal investment in egg capsule volume peaked at an intermediate mating rate. 4. Combining the observed fecundity cost with the apparent benefits of larger offspring size suggests that total female fitness is maximized at an intermediate mating rate. With the latter being close to the natural mating rate of C. sandrana in the field, our findings challenge the assumption of 'male'-driven mating systems in simultaneous hermaphrodites. 5. Our study provides experimental evidence for various mathematical models in which female fitness is maximized at intermediate mating rates.
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Affiliation(s)
- D Sprenger
- Animal Evolutionary Ecology, University of Tübingen, Auf der Morgenstelle 28, 72076 Tübingen, Germany.
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Anthes N, Schulenburg H, Michiels NK. EVOLUTIONARY LINKS BETWEEN REPRODUCTIVE MORPHOLOGY, ECOLOGY AND MATING BEHAVIOR IN OPISTHOBRANCH GASTROPODS. Evolution 2008; 62:900-16. [DOI: 10.1111/j.1558-5646.2008.00326.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Putz A, Michiels NK, Anthes N. Mating Behaviour of the Sperm Trading Sea Slug Chelidonura hirundinina: Repeated Sex Role Alternation Balances Reciprocity. Ethology 2008. [DOI: 10.1111/j.1439-0310.2007.01440.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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Gender-role alternation in the simultaneously hermaphroditic freshwater snail Physa acuta: not with the same partner. Behav Ecol Sociobiol 2007. [DOI: 10.1007/s00265-007-0496-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Schmitt V, Anthes N, Michiels NK. Mating behaviour in the sea slug Elysia timida (Opisthobranchia, Sacoglossa): hypodermic injection, sperm transfer and balanced reciprocity. Front Zool 2007; 4:17. [PMID: 17610714 PMCID: PMC1934903 DOI: 10.1186/1742-9994-4-17] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2007] [Accepted: 07/04/2007] [Indexed: 11/25/2022] Open
Abstract
BACKGROUND In simultaneous hermaphrodites with copulation and internal fertilization it is often unclear whether reciprocal sperm exchange results from the unconditional willingness of both partners to donate and receive sperm, or whether it follows from a more controlled process such as conditional reciprocal sperm exchange, i.e. sperm trading. While in some sea slugs mating is assumed to be based on sperm trading, it seems to be unconditional in others. Here, we describe the unusual mating behaviour of Elysia timida, a small sacoglossan, focussing on indications for conditional reciprocity. RESULTS E. timida shows an as yet unique combination of a long series of hypodermic transfers followed by a short phase with standard insemination into a female genital aperture. Hypodermic transfer takes place in the form of repeated small injections into the dorsal surface of the partner, interrupted by synchronised circling movements. In the final mating phase sperm is transferred into the female genital aperture in a short period. In both phases the two mating individuals show a high degree of transfer symmetry and synchrony. While total duration and number of transfers were balanced within pairs, they varied significantly between pairs. Furthermore, looking at individual hypodermic transfers within pairs, reciprocal transfers lasted longer than unilateral transfers. Final sperm transfers were always reciprocal except for two cases which also diverted from the usual pattern in ways that were suggestive of a conflict over reciprocity. CONCLUSION Our results suggest that individual mating decisions in E. timida depend on what the partner does, indicating conditional reciprocity. If hypodermic transfers also involve the transfer of sperm (which remains to be confirmed), this system represents an up to now unique transition stage between hypodermic and standard insemination, both of which are widespread in this group of sea slugs, but never have been observed to co-occur within the same species.
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Affiliation(s)
- Valerie Schmitt
- Evolutionary Biology, University Muenster, Huefferstrasse 1, 49149 Muenster, Germany
| | - Nils Anthes
- Evolutionary Biology, University Muenster, Huefferstrasse 1, 49149 Muenster, Germany
| | - Nico K Michiels
- Evolutionary Biology, University Muenster, Huefferstrasse 1, 49149 Muenster, Germany
- Zoological Institute, Animal Evolutionary Ecology, Auf der Morgenstelle 28, 72076 Tuebingen, Germany
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Sex role preferences, gender conflict and sperm trading in simultaneous hermaphrodites: a new framework. Anim Behav 2006. [DOI: 10.1016/j.anbehav.2005.09.017] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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