Microsatellite support for active inbreeding in a cichlid fish.

In wild animal populations, the degree of inbreeding differs between species and within species between populations. Because mating with kin often results in inbreeding depression, observed inbreeding is usually regarded to be caused by limited outbreeding opportunities due to demographic factors like small population size or population substructuring. However, theory predicts inclusive benefits from mating with kin, and thus part of the observed variation in inbreeding might be due to active inbreeding preferences. Although some recent studies indeed report kin mating preferences, the evidence is still highly ambiguous. Here, we investigate inbreeding in a natural population of the West African cichlid fish Pelvicachromis taeniatus which showed clear kin mating preferences in standardized laboratory experiments but no inbreeding depression. The presented microsatellite analysis reveals that the natural population has, in comparison to two reference populations, a reduced allelic diversity (A = 3) resulting in a low heterozygosity (H(o) = 0.167) pointing to a highly inbred population. Furthermore, we found a significant heterozygote deficit not only at population (F(is) = 0.116) but also at subpopulation level (F(is) = 0.081) suggesting that inbreeding is not only a by-product of population substructuring but possibly a consequence of behavioral kin preferences.

Male mate choice scales female ornament allometry in a cichlid fish.

BACKGROUND: Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, still remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in Pelvicachromis taeniatus, a biparental cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males. RESULTS: We show that allometry of the female pelvic fin is scaled more positively in comparison to other fins. The pelvic fin exhibits isometry, whereas the other fins (except the caudal fin) show negative allometry. The size of the pelvic fin might be exaggerated by male choice because males prefer female stimuli that show a larger extension of the trait. Female pelvic fin size is correlated with individual condition, suggesting that males can assess direct and indirect benefits. CONCLUSIONS: The absence of positive ornament allometry might be a result of sexual selection constricted by natural selection: fins are related to locomotion and thus may be subject to viability selection. Our study provides evidence that male mate choice might scale the expression of a female sexual ornament, and therefore has implications for the understanding of the relationship of female sexual traits with body size in species with conventional sex-roles.

You can't always get what you want: size assortative mating by mutual mate choice as a resolution of sexual conflict.

BACKGROUND: Assortative mating patterns for mate quality traits like body size are often observed in nature. However, the underlying mechanisms that cause assortative mating patterns are less well known. Sexual selection is one important explanation for assortment, suggesting that i) one (usually the female) or both sexes could show preferences for mates of similar size or ii) mutual mate choice could resolve sexual conflict over quality traits into assortment. We tested these hypotheses experimentally in the socially monogamous cichlid fish Pelvicachromis taeniatus, in which mate choice is mutual. RESULTS: In mate choice experiments, both sexes preferred large mates irrespective of own body size suggesting mating preferences are not size-assortative. Especially males were highly selective for large females, probably because female body size signals direct fitness benefits. However, when potential mates were able to interact and assess each other mutually they showed size-assortative mating patterns, i.e. the likelihood to mate was higher in pairs with low size differences between mates. CONCLUSION: Due to variation in body size, general preferences for large mating partners result in a sexual conflict: small, lower quality individuals who prefer themselves large partners are unacceptable for larger individuals. Relative size mismatches between mates translate into a lower likelihood to mate, suggesting that the threshold to accept mates depends on own body size. These results suggest that the underlying mechanism of assortment in P. taeniatus is mutual mate choice resolving the sexual conflict over mates, rather than preference for mates of similar size.

Olfactory self-recognition in a cichlid fish.

Animal self-cognizance might be of importance in different contexts like territoriality, self-referent mate-choice or kin recognition. We investigated whether the cichlid fish Pelvicachromis taeniatus is able to recognize own olfactory cues. P. taeniatus is a cave breeding fish with pronounced brood care and social behavior. In the experiments we gave male cave owners the choice between two caves in which we introduced scented water. In a first experiment males preferred caves with their own odor over caves with the odor of an unfamiliar, unrelated male. To examine whether self-recognition is based rather on individual or on family cues we conducted two further experiments in which males could choose between their own odor and the odor of a familiar brother and between the odor of a familiar brother and an unfamiliar, unrelated male, respectively. Males preferred their own odor over that of a familiar brother suggesting individual self-referencing. Interestingly, males (at least outbred ones) preferred the odor of an unfamiliar, unrelated male over that of a familiar brother, maybe to avoid competition with kin. We discuss the results in the context of animal self-cognizance. All experiments were conducted with in- and outbred fish. Inbreeding did not negatively affect self-recognition.

Fish odour triggers conspecific attraction behaviour in an aquatic invertebrate.

Group living has evolved as an adaptation to predation in many animal species. In a multitude of vertebrates, the tendency to aggregate varies with the risk of predation, but experimental evidence for this is less well known in invertebrates. Here, we examine the tendency to aggregate in the freshwater amphipod Gammarus pulex in the absence and presence of predator fish odour. Without fish odour, the gammarids showed no significant tendency to aggregate. In contrast to this, in fish-conditioned water, they significantly preferred to stay close to conspecifics. Predation risk can, thus, influence gammarids social behaviour.

Female mating preference for own males on species and population level in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae).

Chromaphyosemion killifishes are a very promising taxon for the examination of general principles and mechanisms underlying speciation. The polygamous mating system and high degree of sexual dimorphism in this group suggest that sexual selection and female mating preferences play a crucial role in the current radiation process. Because the emergence of mating preferences for individuals of the own population during allopatry is a necessary precondition for speciation by sexual selection, either via diverging mate recognition traits or reinforcement, we examined whether females of different nominal species (Chromaphyosemion bivittatum vs. Chromaphyosemion volcanum) or populations (C. bivittatum "Toko" vs. C. bivittatum "Ilor") prefer their own males as mating partners. For this purpose, two different methods were used. First, we conducted simultaneous choice tests where females could choose between two different males, and second, we counted the eggs produced by females in consecutive matings with different males. Both approaches produced the same result: females of the populations under examination preferred to mate with their own males. Preference for own males was symmetrical in all tests. Males, on the other hand, do not discriminate between females, not even on the level of nominal species. Thus, our results are in accordance with the hypothesis that female choice is an important factor for speciation in Chromaphyosemion. Additionally, we present some preliminary data on post-zygotic isolation between the populations.

Extraordinarily long sperm in the socially monogamous cichlid fish Pelvicachromis taeniatus.

The main function of the spermatozoon is the transfer of the male haploid genome during fertilisation. In animals in general and in fishes in particular, there is huge variation in sperm size. In fishes, sperm size ranges from 13 microm in Mugil cephlus to nearly 100 microm in the channel catfish Ictalurus punctatus. We examined intra-specific variation in sperm morphometry in the socially monogamous cichlid Pelvicachromis taeniatus using scanning electron microscopy. The mean total sperm length of nearly 70 microm was extraordinarily large for cichlids. Furthermore, within-male variation was remarkably high. To our knowledge, P. taeniatus produces the longest cichlid sperm ever documented. Several hypotheses concerning the adaptive significance of these results are presented.

Active inbreeding in a cichlid fish and its adaptive significance.

Levels of inbreeding are highly variable in natural populations. Inbreeding can be due to random factors (like population size), limited dispersal, or active mate choice for relatives. Because of inbreeding depression, mating with kin is often avoided, although sometimes intermediately related individuals are preferred (optimal outbreeding). However, theory predicts that the advantages of mating with close kin can override the effects of inbreeding depression, but in the animal kingdom, empirical evidence for this is scarce. Here we show that both sexes of Pelvicachromis taeniatus, an African cichlid with biparental brood care, prefer mating with unfamiliar close kin over nonkin, suggesting inclusive fitness advantages for inbreeding individuals. Biparental care requires synchronous behavior among parents. Since parental care is costly, there is a conflict between parents over care, which can reduce offspring fitness. Relatedness is expected to enhance cooperation among individuals. The comparison of the parental behavior of in- and outbreeding pairs showed that related parents were more cooperative and invested more than unrelated parents. Since we found no evidence for inbreeding depression, our results suggest that in P. taeniatus, inbreeding is an advantageous strategy.

Infection with an acanthocephalan manipulates an amphipod's reaction to a fish predator's odours.

Many parasites with complex life cycles increase the chances of reaching a final host by adapting strategies to manipulate their intermediate host's appearance, condition or behaviour. The acanthocephalan parasite Pomphorhynchus laevis uses freshwater amphipods as intermediate hosts before reaching sexual maturity in predatory fish. We performed a series of choice experiments with infected and uninfected Gammarus pulex in order to distinguish between the effects of visual and olfactory predator cues on parasite-induced changes in host behaviour. When both visual and olfactory cues, as well as only olfactory cues were offered, infected and uninfected G. pulex showed significantly different preferences for the predator or the non-predator side. Uninfected individuals significantly avoided predator odours while infected individuals significantly preferred the side with predator odours. When only visual contact with a predator was allowed, infected and uninfected gammarids behaved similarly and had no significant preference. Thus, we believe we show for the first time that P. laevis increases its chance to reach a final host by olfactory-triggered manipulation of the anti-predator behaviour of its intermediate host.

Karyotype differentiation in Chromaphyosemion killifishes (Cyprinodontiformes, Nothobranchiidae). I: Chromosome banding patterns of C. alpha, C. kouamense and C. lugens.

The karyotypes of three recently described species of Chromaphyosemion, namely C. lugens, C. alpha and C. kouamense, were analysed using conventional Giemsa staining, C-banding and sequential banding (fluorescence banding with 4', 6-diamidino-2-phenylindole (DAPI) and Chromomycin A(3) (CMA(3)), C-banding, AgNO(3)-staining). Diploid chromosome numbers ranged from 2n = 36 in C. lugens to 2n = 38 in C. alpha and C. kouamense. The karyotype of C. lugens consisted of one pair of metacentric (m) and 17 pairs of telocentric (t) chromosomes, that of C. alpha was composed of one pair of submetacentric (sm), six pairs of subtelocentric (st) and 12 pairs of t chromosomes, and that of C. kouamense comprised five pairs of st and 14 pairs of t chromosomes. In addition to the differences in karyotype structures and/or chromosome numbers, the karyotypes of the examined species differed with respect to NOR phenotype and distribution and base composition of heterochromatin. No heteromorphic sex chromosomes were detected in any of the species. Our findings provide cytotaxonomic evidence for the species distinctness of C. alpha, C. kouamense and C. lugens whose descriptions were based primarily on external morphology.