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Background: In many species males face a higher predation risk than females because males display elaborate traits that evolved under sexual selection, which may attract not only females but also predators. Females are, therefore, predicted to avoid such conspicuous males under predation risk. The present study was designed to investigate predator-induced changes of female mating preferences in Atlantic mollies (Poecilia mexicana). Males of this species show a pronounced polymorphism in body size and coloration, and females prefer large, colorful males in the absence of predators.
Results: In dichotomous choice tests predator-naive (lab-reared) females altered their initial preference for larger males in the presence of the cichlid Cichlasoma salvini, a natural predator of P. mexicana, and preferred small males instead. This effect was considerably weaker when females were confronted visually with the non-piscivorous cichlid Vieja bifasciata or the introduced non-piscivorous Nile tilapia (Oreochromis niloticus). In contrast, predator experienced (wild-caught) females did not respond to the same extent to the presence of a predator, most likely due to a learned ability to evaluate their predators' motivation to prey.
Conclusions: Our study highlights that (a) predatory fish can have a profound influence on the expression of mating preferences of their prey (thus potentially affecting the strength of sexual selection), and females may alter their mate choice behavior strategically to reduce their own exposure to predators. (b) Prey species can evolve visual predator recognition mechanisms and alter their mate choice only when a natural predator is present. (c) Finally, experiential effects can play an important role, and prey species may learn to evaluate the motivational state of their predators.
One possible mechanism for the (co-)evolution of seemingly novel male traits and female preferences for them is that males exploit pre-existing female biases, and livebearing fishes (Poeciliidae) have been at the forefront of this research for almost two decades. Here, using 13 poeciliid species from four different genera, we tested whether mustache-like rostral filaments found in males of some Mexican molly (Poecilia sphenops) populations could have evolved due to exploitation of a pre-existing female bias. While Mexican mollies were the only species with a significant female association preference for mustached males, we also did not find any species exhibiting significant aversion for mustached males; rather, variance in female preference scores was large throughout. For example, more than 25% of females spent twice as much time with the mustached male compared to the non-mustached male in most species, but even 31% of Mexican molly females spent more time near the non-mustached male. Hence, a comparison of the strength of preference was inconclusive. We discuss the possibility that the female preference of P. sphenops for mustached males could be due to a female pre-existing bias (sensu lato), even if population means were not significant for species other than P. sphenops. This highlights the importance of distinguishing between population means and individual preferences when interpreting mate choice, and thus, adds depth to the concept of mating preferences as a motor for evolutionary change.
Declines in breeding site fidelity in an increasing population of White Storks Ciconia ciconia
(2011)
Following a steep decline, White Stork Ciconia ciconia populations in Germany are currently increasing, allowing us to examine potential density-dependent effects on breeding dispersal. Our data suggest that the proportion of breeding dispersers has increased over time, indicating a density-dependent component in nest-site fidelity that may be linked to increased competition.
Mate choice copying was mostly described as a strategy employed by females to assess the quality of potential mates, but also males can copy other males' mate choice. An open question in this context is whether and how copying males evaluate sperm competition risk, as mating with a female that has already copulated with another male obviously sets the stage for intense sperm competition (i.e., in species with internal fertilization). Using the livebearing Atlantic molly (Poecilia mexicana) as a model, we asked (a) whether males of that species indeed copy other males' choices, and if they do so, (b) whether copying males strategically adjust their behavior to sperm competition risk. We used an approach where focal males could first choose to associate with a large or a small stimulus female. Mate choice tests were then repeated after an "observation phase" during which either no model male was present (treatment 1, control) or the previously non-preferred female could be seen associating (treatment 2) or physically interacting (treatment 3) with a model male. We found that, after the observation phase, males spent considerably more time with the previously non-preferred female in treatment (2), i.e., they copied the model male's choice. This effect was much weaker during treatment (3) where sexual interactions between the model male and the formerly non-preferred female were allowed. Males, therefore, seem to adjust their copying behavior strategically to the perceived risk of sperm competition.
Mountain gazelles (Gazella gazella) rank among the most critically endangered mammals on the Arabian Peninsula. Past conservation efforts have been plagued by confusion about the phylogenetic relationship among various 'phenotypically discernable' populations, and even the question of species boundaries was far from being certain. This lack of knowledge has had a direct impact on conservation measures, especially ex situ breeding programmes, hampering the assignment of captive stocks to potential conservation units. Here, we provide a phylogenetic framework, based on the analysis of mtDNA sequences (360 bp cytochrome b and 213 bp Control Region) of 126 individuals collected from the wild throughout the Arabian Peninsula and from captive stocks. Our analyses revealed two reciprocally monophyletic genetic lineages within the presumed species Gazella gazella: one 'northern clade' on the Golan Heights (Israel/Syrian border) and one genetically diverse larger clade from the rest of the Arabian Peninsula including the Arava Valley (Negev, Israel). Applying the Strict Phylogenetic Species Concept (sensu Mishler & Theriot, 2000) allows assigning species status to these two major clades.
In most mammals, females are philopatric while males disperse in order to avoid inbreeding. We investigated social structure in a solitary ungulate, the bushbuck Tragelaphus sylvaticus in Queen Elizabeth National Park, Uganda by combining behavioural and molecular data. We correlated spatial and social vicinity of individual females with a relatedness score obtained from mitochondrial DNA analysis. Presumed clan members shared the same haplotype, showed more socio-positive interactions and had a common home range. Males had a higher haplotype diversity than females. All this suggests the presence of a matrilineal structure in the study population. Moreover, we tested natal dispersal distances between male and female yearlings and used control region sequences to confirm that females remain in their natal breeding areas whereas males disperse. In microsatellite analysis, males showed a higher genetic variability than females. The impoverished genetic variability of females at both molecular marker sets is consistent with a philopatric and matrilineal structure, while the higher degree of genetic variability of males is congruent with a higher dispersal rate expected in this sex. Evidence even for male long-distance dispersal is brought about by one male carrying a haplotype of a different subspecies, previously not described to occur in this area.
Background: Local adaptation to divergent environmental conditions can promote population genetic differentiation even in the absence of geographic barriers and hence, lead to speciation. Perturbations by catastrophic events, however, can distort such parapatric ecological speciation processes. Here, we asked whether an exceptionally strong flood led to homogenization of gene pools among locally adapted populations of the Atlantic molly (Poecilia mexicana, Poeciliidae) in the Cueva del Azufre system in southern Mexico, where two strong environmental selection factors (darkness within caves and/or presence of toxic H2S in sulfidic springs) drive the diversification of P. mexicana. Nine nuclear microsatellites as well as heritable female life history traits (both as a proxy for quantitative genetics and for trait divergence) were used as markers to compare genetic differentiation, genetic diversity, and especially population mixing (immigration and emigration) before and after the flood. Results: Habitat type (i.e., non-sulfidic surface, sulfidic surface, or sulfidic cave), but not geographic distance was the major predictor of genetic differentiation. Before and after the flood, each habitat type harbored a genetically distinct population. Only a weak signal of individual dislocation among ecologically divergent habitat types was uncovered (with the exception of slightly increased dislocation from the Cueva del Azufre into the sulfidic creek, El Azufre). By contrast, several lines of evidence are indicative of increased flood-induced dislocation within the same habitat type, e.g., between different cave chambers of the Cueva del Azufre. Conclusions: The virtual absence of individual dislocation among ecologically different habitat types indicates strong natural selection against migrants. Thus, our current study exemplifies that ecological speciation in this and other systems, in which extreme environmental factors drive speciation, may be little affected by temporary perturbations, as adaptations to physico-chemical stressors may directly affect the survival probability in divergent habitat types.
We investigated herd-sizes and herd-compositions of Impala (Aepyceros melampus) inside a protected area [Lake Mburo National Park (LMNP) in western Uganda] and the unprotected adjacent ranchland [the Ankole Ranching Scheme (ARS)]. Impala experience intense hunting and poaching in the study area, and poaching is especially strong on the ARS. We found evidence for changes in overall group-sizes in both mixed-sex and pure bachelor herds between areas in and outside LMNP. Mixed-sex herds strongly decreased in size outside the National Park, but bachelor herds even slightly increased in size. While the group-composition of mixed-sex herds was very similar in areas in and outside LMNP, bachelor herds comprised more yearlings and subadult males on the ARS. Our study suggests that effects of hunting and other human nuisance may differ between herd types: mixed herds probably decrease in size because females are more strongly hunted. Around LMNP, impala are usually hunted using nets and spears, thereby increasing the hunters' chance of being injured. Poachers therefore prefer hornless females (and their calves), as it is less dangerous to handle net-caught females than males. As a result, males are less hunted, but increased vigilance and, therefore, reduced aggression among the members of a bachelor herd, may account for the observed increase in herd sizes and changes in group-compositions.
Males often face strong mating competition by neighboring males in their social environment. A recent study by Plath et al. (Anim Behav 75:21-29, 2008a) has demonstrated that the visual presence of a male competitor (i.e., an audience male) affects the expression of male mating preferences in a poeciliid fish (Poecilia mexicana) with a weaker expression of mating preferences when an audience male observed the focal male. This may be a tactic to reduce sperm competition, since surrounding males likely share intrinsic preferences for female traits or copy mate choice decisions. Here, we examined the hypothesis that a same-sex audience would affect female mate preferences less than male mating preferences. Our hypothesis was based on the assumptions that (1) competition for mates in a fashion that would be comparable in strength to sperm competition or overt male-male aggression is absent among Poecilia females, and (2) P. mexicana females typically form female-biased shoals, such that almost any female mate choice in nature occurs in front of a female audience. Poecilia females (P. mexicana, surface and cave form, and the closely related gynogenetic Poecilia formosa) were given a choice between a large and a small male, and the tests were repeated while a conspecific, a heterospecific, or no audience female (control) was presented. Females spent more time in the neutral zone and, thus, less time near the males during the second part of a trial when an audience was presented, but-consistent with predictions-females showed only slightly weaker expression of mate preferences during the second part of the tests. This decline was not specific to the treatment involving an audience and was significantly weaker than the effect seen in the male sex.