Michael Taborsky

Sperm competition in fish: `bourgeois' males and parasitic spawning

Fish exhibit an enormous variety of reproductive patterns. There is external and internal fertilization, simultaneous and sequential hermaphroditism as well as gonochorism, and an extremely widespread occurrence of parasitic reproductive behaviour among males. In most fish species there is a great size range of reproductive males, setting the stage for divergent, intraspecific reproductive patterns and an unparalleled concentration of alternative male reproductive phenotypes. Recent theoretical, empirical and comparative evidence suggests that adaptations to sperm competition in fish might be responsible for some of the most intriguing examples of reproductive design known.

Alternative Reproductive Tactics: An Integrative Approach

Preface Rui F. Oliveira, Michael Taborsky and H. Jane Brockmann 1. The evolution of alternative mating tactics: concepts and questions Michael Taborsky, Rui F. Oliveira and H. Jane Brockmann Part I. Ultimate Causes and Origins of ARTs: 2. Alternative reproductive tactics and the evolution of alternative allocation phenotypes H. Jane Brockmann and Michael Taborsky 3. Phylogenetic analysis of alternative reproductive tactics - Problems and possibilities Vitor C. Almada and Joana I. Robalo 4. Modeling alternative mating tactics as dynamic games Jeffrey R. Lucas and Richard D. Howard Part II. Proximate Mechanisms of ARTs: 5. The roles of genes and the environment in the expression and evolution of alternative tactics Douglas J. Emlen 6. Neuroendocrine mechanisms of alternative reproductive tactics: the chemical language of reproductive and social plasticity Andrew H. Bass and Paul M. Forlano 7. Hormones and alternative reproductive tactics in vertebrates Rui F. Oliveira, Adelino V. M. Canario and Albert F. H. Ros Part III. Taxonomic Reviews of ARTs: 8. Alternative reproductive tactics in insects H. Jane Brockmann 9. The expression of crustacean mating strategies Stephen M. Shuster 10. Alternative reproductive tactics in fish Michael Taborsky 11. Alternative reproductive tactics in amphibians Kelly R. Zamudio and Lauren M. Chan 12. Alternative reproductive tactics in reptiles Ryan Calsbeek and Barry Sinervo 13. Alternative reproductive tactics in birds Oliver Kruger 14. Alternative reproductive tactics in nonprimate male mammals Jerry O. Wolff 15. Alternative reproductive tactics in primates Joanna M. Setchell Part IV. Emerging Perspectives on ARTs: 16. Communication and the evolution of alternative reproductive tactics David Goncalves, Rui F. Oliveira and Peter K. McGregor 17. Alternative mating tactics and mate choice for good genes or good care Brian Neff 18. Conflict between the sexes and alternative reproductive tactics within a sex Suzanne H. Alonzo 19. Cooperative breeding as an alternative reproductive tactic Walter D. Koenig and Janis L. Dickinson 20. Integrating mechanisms and function: prospects for future research H. Jane Brockmann, Rui Oliveira and Michael Taborsky.

Helpers in fish

SummaryField data show that in the cichlid fish Lamprologus brichardi conspecifics other than the reproducing pair help in brood care and territory maintenance. The expected degree of relatedness between helpers and the eggs or larvae they tend lies between 0.25 and 0.5, decreasing with the helpers age. This decrease might influence the point of time at which helpers depart. Five other endemic Lake Tanganyika cichlids showing rather similar helping behaviour are described.

Correlates of group size in a cooperatively breeding cichlid fish (Neolamprologus pulcher)

Abstract. Neolamprologus pulcher, a cooperatively breeding cichlid fish from Lake Tanganyika, lives in permanent social groups comprising one breeding pair and helpers of both sexes. Variation in group size (1–14 helpers) provides an opportunity to investigate factors that affect how many helpers remain in a group and in turn how group size affects reproductive success. This field study showed that larger groups live in larger territories with more shelter. Group size was more strongly correlated with territory quality than with breeder size. Experimental enhancement of territory quality did not affect group size but group size decreased when territory quality was reduced. Breeders living in a large group benefit because such individuals feed more often and have lower workloads and greater reproductive success. Helpers in larger groups also fed more frequently but did not have lower workloads. This is one of the first experimental studies to examine the factors influencing group size in cooperative breeders.

Generalized Reciprocity in Rats

The evolution of cooperation among nonrelatives has been explained by direct, indirect, and strong reciprocity. Animals should base the decision to help others on expected future help, which they may judge from past behavior of their partner. Although many examples of cooperative behavior exist in nature where reciprocity may be involved, experimental evidence for strategies predicted by direct reciprocity models remains controversial; and indirect and strong reciprocity have been found only in humans so far. Here we show experimentally that cooperative behavior of female rats is influenced by prior receipt of help, irrespective of the identity of the partner. Rats that were trained in an instrumental cooperative task (pulling a stick in order to produce food for a partner) pulled more often for an unknown partner after they were helped than if they had not received help before. This alternative mechanism, called generalized reciprocity, requires no specific knowledge about the partner and may promote the evolution of cooperation among unfamiliar nonrelatives.

Alternative Reproductive Tactics: The evolution of alternative reproductive tactics: concepts and questions

Here we outline the meaning of the term alternative reproductive tactics, or ARTs, and discuss why the existence of ARTs is so widespread in animals. We ask what we need to know to understand the evolution of ARTs and the importance of general principles such as frequency dependence, density dependence, and condition dependence, and what we need to know about proximate mechanisms involved in the regulation of ARTs to comprehend evolutionary patterns. We discuss current issues in the study of ARTs and list 12 questions that we think need particular attention. Throughout we shall provide representative examples of ARTs in animals to illustrate the ubiquitous nature of this phenomenon.

A test of the ‘challenge hypothesis’ in cichlid fish: simulated partner and territory intruder experiments

In male birds, the responsiveness of androgens to sexual and territorial behaviour is predicted to vary with mating system and the degree of paternal investment (‘challenge hypothesis’, CH; Wingfield et al. 1990, American Naturalist, 136, 829–846). The CH predicts a higher and longer lasting ‘breeding baseline’ androgen level in males of polygynous species with no or only short-term paternal investment than in males of monogamous species with a high degree of paternal investment. Since the applicability of the CH to nonavian vertebrates has been unclear, we experimentally tested its predictions in several cichlid fish (Neolamprologus pulcher, Lamprologus callipterus, Tropheus moorii, Pseudosimochromis curvifrons and Oreochromis mossambicus) using a simulated territorial intruder protocol. Androgens (11-ketotestosterone: 11-KT; testosterone: T) were measured from fish-holding water. In all species sampled, the 11-KT patterns confirmed the predictions of the CH originating from the avian literature, but T patterns did not. Males of all species sampled were highly responsive to territorial intrusions; however, the magnitude and duration of this response, that is, the rapid return to baseline 11-KT levels, could not clearly be explained by the degree of paternal care. 11-KT responses to interactions with ovulating females were observed in maternal mouthbrooders but not in biparental species (e.g. Lamprologini). At the interspecific level, androgen responsiveness was greater among males of monogamous species, as predicted, but also in species with more intense pair bonding (e.g. Tropheus moorii). Thus, this study confirms the predictions of the CH in cichlid fish at both the intraspecific and the interspecific levels.

Do woodpecker finches acquire tool-use by social learning?

Tool–use is widespread among animals, but except in primates the development of this behaviour is poorly known. Here, we report on the first experimental study to our knowledge of the mechanisms underlying the acquisition of tool–use in a bird species. The woodpecker finch Cactospiza pallida, endemic to the Galápagos Islands, is a famous textbook example of tool–use in animals. This species uses modified twigs or cactus spines to pry arthropods out of tree holes. Using nestlings and adult birds from the field, we tested experimentally whether woodpecker finches learn tool–use socially. We show that social learning is not essential for the development of tool–use: all juveniles developed tool–use regardless of whether or not they had a tool–using model. However, we found that not all adult woodpecker finches used tools in our experiments. These non–tool–using individuals also did not learn this task by observing tool–using conspecifics. Our results suggest that tool–use behaviour depends on a very specific learning disposition that involves trial–and–error learning during a sensitive phase early in ontogeny.

Predation risk is an ecological constraint for helper dispersal in a cooperatively breeding cichlid.

Environmental conditions are thought to be responsible for the extent and benefits of cooperative breeding in many animal societies, but experimental tests are scarce. We manipulated predator pressure in the cooperatively breeding cichlid Neolamprologus pulcher in Lake Tanganyika, where predators have been suggested to influence helper and breeder survival, helper dispersal and group reproductive success. We varied the type and intensity of predation by releasing medium, large, or no predators inside large underwater cages enclosing two or three group territories. Helper and breeder survival, helper dispersal and group reproductive success decreased from the control, to the medium– and large–predator treatments. These effects were modified by helper body size and the number of adults protecting the group from predators, supporting the ‘group augmentation hypothesis’. Predators forced helpers to stay closer to, and spend more time inside, protective shelters. The results demonstrate the importance of predators for group living in this species, and support the ‘ecological constraints hypothesis’ of cooperative breeding, in the sense that subordinates stay at home rather than leave and breed independently under the risk of predation.

Evolution of cooperation by generalized reciprocity

The evolution of cooperation by direct reciprocity requires that individuals recognize their present partner and remember the outcome of their last encounter with that specific partner. Direct reciprocity thus requires advanced cognitive abilities. Here, we demonstrate that if individuals repeatedly interact within small groups with different partners in a two person Prisoners Dilemma, cooperation can emerge and also be maintained in the absence of such cognitive capabilities. It is sufficient for an individual to base their decision of whether or not to cooperate on the outcome of their last encounter—even if it was with a different partner.