Predator-induced changes of male and female mating preferences: innate and learned components

Predator exposure early in life shapes behavioral development and individual variation in a clonal fish

Predation risk is one of the most important factors generating behavioral differences among populations. In addition, recent attention focusses on predation as a potential driver of patterns of individual behavioral variation within prey populations. Previous studies provide mixed results, reporting either increased or decreased among-individual variation in response to risk. Here, we take an explicit developmental approach to documenting how among-individual variation develops over time in response to predator exposure, controlling for both genetic and experiential differences among individuals. We reared juveniles of naturally clonal Amazon mollies, Poecilia formosa, either with or without a predator visible during feedings over 4 weeks and analyzed activity during feedings, time spent feeding and number of visits to the feeding spot. (I) Predator-exposed fish did not differ from control fish in average feeding behavior, but they were less active during feeding trials. (II) In the absence of the predator, substantial changes in among-individual variation over time were detected: among-individual differences in feeding duration increased whereas differences in activity decreased, but there were no changes in feeder visits. In contrast, in the presence of a predator, among-individual variation in all three behaviors was stable over time and often lower compared to control conditions. Our work suggests that predation risk may have an overall stabilizing effect on the development of individual variation and that differences in predation risk may well lead to population-wide differences in among-individual behavioral variation.

Strength of female mate preferences in temperature manipulation study supports the signal reliability hypothesis

Both sexually selected traits and mate preferences for these traits can be context dependent, yet how variation in preferred traits could select for context dependent preferences has rarely been examined. The signal reliability hypothesis predicts that mate preferences vary across contexts (e.g., environments) in relation to the reliability of the information preferred traits provide in those contexts. Extensive variation in copy number of mc4r B alleles on the Y-chromosome that associates with male size in Xiphophorus multilineatus allowed us to use a split-sibling design to determine if male size is more likely to provide information about male genotype (i.e., dam) when males were reared in a warm as compared to a cold environment. We then examined strength of preference for male size by females reared in the same two environments. We found that males were larger in the cold environment, but male size was more variable across dams in the warm environment, and therefore male size would be a more reliable indicator of dam (i.e., genetics) in the warm environment. Females reared in the warm environment had stronger mate preferences based on male size than cold reared females, with a significant influence of dam on strength of preference. Therefore, strength of female preference for male size was influenced by the temperature in which they were reared, with the direction of the difference across treatments supporting the signal reliability hypothesis. Understanding how the reliability of male traits can select for contextual variation in the strength of the female mate preferences will further our discovery of adaptive mate preferences. For example, a relationship between the strength of a female's mate preference and their growth rates was detected in the context where females had a preference based on male size, supporting a hypothesis from previous work with this species of disassortative mating in relation to growth rates to mitigate a documented growth-mortality tradeoff.

Increasing salinization of freshwater limits invasiveness of a live-bearing fish: Insights from behavioral and life-history traits

Biological invasions and continued salinization of freshwater are two global issues with largely serious ecological consequences. Increasing salinity in freshwater systems, as an environmental stressor, may negatively affect normal life activities in fish. It has been documented that salinity limits the invasive success of alien species by mediating physiological and life-history performances, however, there are few studies on how salinity affects its invasive process via altered behaviors. Using wild-caught invasive western mosquitofish (Gambusia affinis) as animal model, in this study, we asked whether gradual increasing salinity affects behaviors (personality and mate choice decision here), life-history traits, as well as the correlation between them by exposing G. affinis to three levels salinity (freshwater, 10 and 20‰). Results showed that, with increased salinity, male tended to be shyer, less active, less sociable, and reduced desire to mate, and female tended to be shyer, less active and lost preferences for the larger male. Furthermore, across salinity treatments, male exhibited reduced body fat content and rising reproduction allocation, however, pregnant female revealed diametrically opposed trends. In addition, the correlation between life-history traits and behaviors was only identified in pregnant female. It seems that either salinity or life-history traits directly affects mosquitofish behaviors. In summary, our results partially emphasize the harmful consequences of salinity on both life-history traits and behavioral performances. These findings provide a novel perspective on how salinity potentially affect fish fitness via altering personalities, mate choice decisions, as well as body condition, and hence supports the idea that salinity could affect the spread of invasive mosquitofish.

Effect of bio-insecticide residues and the presence of predatory cues on mating in a biocontrol spider

Insecticide formulations can cause mortality in natural enemies or have sublethal effects on them, which include alterations in their behaviour and development. Here, we investigated the effect of a bioinsecticide (azadirachtin) and predator cues on mating in a biocontrol spider, Philodromus cespitum. Firstly, adult males were exposed to cues from ants (as predators) or conspecific juveniles (as controls) and those from virgin adult females combined with insecticide residues and we then recorded their selection of the respective surfaces. In an insecticide-free environment, males spent significantly more time on the surface with cues from juveniles and virgin females than on the surface with cues from ants and virgin females. In the environment with ant cues, males did not spend significantly more time on the surface treated with water or insecticide residues. Secondly, adult male and female spiders were exposed to cues from predators and conspecifics and fresh insecticide residuals and we recorded mating behaviour. The presence of ant cues nor the presence of insecticide residues had a significant effect on the mating behaviour. However, the frequency of females biting males was significantly lower on the surface with insecticide residues and ant cues and highest on the surface with ant cues and water treatment. The size of mating plugs (applied to female genitals by males during mating) was not different between ant cues and control, but the plugs were significantly larger on the surface with insecticide residues. We conclude that azadirachtin affected only slightly the perception of predation risk and consequently mating behaviour in P. cespitum. Similarly, presence of ant cues had little effect on mating.

Sight of parasitoid wasps accelerates sexual behavior and upregulates a micropeptide gene in Drosophila

Parasitoid wasps inflict widespread death upon the insect world. Hundreds of thousands of parasitoid wasp species kill a vast range of insect species. Insects have evolved defensive responses to the threat of wasps, some cellular and some behavioral. Here we find an unexpected response of adult Drosophila to the presence of certain parasitoid wasps: accelerated mating behavior. Flies exposed to certain wasp species begin mating more quickly. The effect is mediated via changes in the behavior of the female fly and depends on visual perception. The sight of wasps induces the dramatic upregulation in the fly nervous system of a gene that encodes a 41-amino acid micropeptide. Mutational analysis reveals that the gene is essential to the behavioral response of the fly. Our work provides a foundation for further exploration of how the activation of visual circuits by the sight of a wasp alters both sexual behavior and gene expression.

You're Just My Type: Mate Choice and Behavioral Types

Consistent individual differences in behavior [i.e., behavioral types (BTs)], are common across the animal kingdom. Consistency can make behavior an adaptive trait for mate choice decisions. Here, we present a conceptual framework to explain how and why females might evaluate a male's BT before mating. Because BTs are consistent across time or context, a male's BT can be a reliable indicator of his potential to provide direct benefits. Heritable BTs can enable informed mate choice via indirect benefits. Many key issues regarding patterns of mate choice, including sensory biases, context dependence, and assortative mating apply to BT-dependent mate choice. Understanding the relationship between BTs and mate choice may offer insights into patterns of variation and consistency common in behavioral traits.

Geographical and temporal variation of multiple paternity in invasive mosquitofish (Gambusia holbrooki, Gambusia affinis)

Multiple paternity (MP) increases offspring's genetic variability, which could be linked to invasive species' evolvability in novel distribution ranges. Shifts in MP can be adaptive, with greater MP in harsher/colder environments or towards the end of the reproductive season, but climate could also affect MP indirectly via its effect on reproductive life histories. We tested these hypotheses by genotyping N = 2,903 offspring from N = 306 broods of two closely related livebearing fishes, Gambusia holbrooki and Gambusia affinis. We sampled pregnant females across latitudinal gradients in their invasive ranges in Europe and China, and found more sires per brood and a greater reproductive skew towards northern sampling sites. Moreover, examining monthly sampling from two G. affinis populations, we found MP rates to vary across the reproductive season in a northern Chinese, but not in a southern Chinese population. While our results confirm an increase of MP in harsher/more unpredictable environments, path analysis indicated that, in both cases, the effects of climate are likely to be indirect, mediated by altered life histories. In both species, which rank amongst the 100 most invasive species worldwide, higher MP at the northern edge of their distribution probably increases their invasive potential and favours range expansions, especially in light of the predicted temperature increases due to global climate changes.