The causes and consequences of kin recognition in the cooperatively breeding cichlid Neolamprologus pulcher

QL Zoology

Le Vin, Ashley ; Arnold, Kate E.

University:University of Glasgow

关键词: cooperative breeding, kin recognition, behavioural ecology, evolutionary biology, cichlid, fish, inbreeding, personality, microsatellites, Neolamprologus pulcher, Xiphophorus hellerii, phenotype matching, mate choice;   

Others  :  http://theses.gla.ac.uk/2333/1/2010LeVinnPhD.pdf

来源: University of Glasgow

【 摘 要 】

Kin recognition allows individuals to assess their relatedness to conspecifics, thus they may then show kin discrimination and make informed choices as to with whom to associate and/or breed. Cooperatively breeding species, such as the cichlid Neolamprologus pulcher, are an excellent model system for investigating kin recognition, as they live in complex social groups, containing both kin and non-kin group members. Cooperation involves individuals helping to rear the offspring of the dominant pair. Helping is costly, but helpers may gain direct fitness benefits through living in a group, and if they aid relatives, they can also gain indirect fitness benefits through kin selection. Furthermore, by being able to recognise kin, individuals can also avoid inbreeding and the potentially deleterious consequences of it. Thus, N. pulcher are predicted to have good kin recognition abilities. In this thesis, I investigate kin recognition and its consequences for helping and mate choice in a captive population of N. pulcher. In chapter 2, I investigated the kin recognition capabilities of juvenile N. pulcher whilst controlling for familiarity. I found that N. pulcher preferred to associate with unfamiliar kin over unfamiliar non-kin. Kin recognition was via some form of phenotype matching, with chemical cues being more important than visual cues. Additionally, I found no discrimination between familiar and unfamiliar kin; thus, relatedness rather than familiarity was important in the association preferences of juvenile N. pulcher. Chapter 3 explored whether relatedness to the breeding pair, or differences in individual behavioural types affected the amount or type of helping shown by N. pulcher. Controlling for group size and helper relatedness, I found that the relatedness of the helpers to the breeders had no influence on the amount or type of help carried out. Thus, kin selected benefits alone cannot explain variation in helping behaviour in N. pulcher. The amount of territory maintenance carried out correlated with the amount of territory defence, thus, some individuals were consistently helpful. Individuals varied consistently in their aggressiveness, risk-responsiveness and activity levels, but these traits did not correlate with one another. More aggressive, risk-prone or more active helpers carried out more territory defence than submissive, risk-averse or inactive helpers. In contrast, the amount of territory maintenance carried out by helpers, was not correlated with the behavioural types. Thus, differences in behavioural types explained more variation in helping behaviour in N. pulcher than relatedness. Since motivation to associate with kin might vary with age and individual state, in chapter 4, I investigated whether N. pulcher avoided kin when sexually mature, and examined the fitness consequences of inbreeding. In standard two-way choice tests, I found that whilst male N. pulcher showed no preferences for associating with sisters over female non-kin, female N. pulcher preferred to associate with brothers over male non-kin. However, when given the opportunity to breed, latency to breed and hatching success did not differ between brother-sister pairs and unrelated pairs. Thus, in N. pulcher inbreeding is not actively avoided and does not appear to be detrimental to fitness. I suggest that sex-biased dispersal and regular breeder replacement on territories may minimise the occurrences of inbreeding in the wild and that inbreeding may be opportunistic, rather than a strategic decision. The final theme of my thesis investigated the effect of phenotypic traits on mate choice. In N. pulcher (chapter 4) I found that the size of an individual’s facial stripe, which varies between individuals, played no role in mate association preferences. I then investigated male mate choice for female body size in the non-cooperatively breeding green swordtail, Xiphophorus hellerii. In chapter 5, I found that males showed preferences for large over small females when presented only with visual cues, but not with only chemical cues. However, as the size differential between the large and small female increased, males showed preferences for the larger female based on chemical cues. So, male X. hellerii prefer larger females, which are predicted to be more fecund and hence, bring them greater fitness returns. In conclusion, my study has shown that N. pulcher can recognise kin, but the ability to do this does not compel individuals to show kin directed cooperation, or inbreeding avoidance. Instead, factors such as an individual’s behavioural type have more influence on decisions to help, and inbreeding does not appear to be detrimental to fitness. Overall, this project shows that under the conditions we tested, kin selection alone does not drive the social interactions in N. pulcher groups. Further, it highlights the need to consider multiple factors affecting an individual’s fitness, in order to fully understand why different species show a propensity to recognise and discriminate between kin and non-kin.