Phenotype-dependent mate choice in Propylea dissecta and its fitness consequences

The better, the choosier: A meta-analysis on interindividual variation of male mate choice

Male mate choice occurs in several animal species, but we know little about the factors that influence the expression of this behaviour. Males vary in their capacity to acquire mates (i.e. male quality), which could be crucial to male mate choice expression but it is often overlooked. Using a meta‐analytical approach, we explore interindividual variation in the expression of male mate choice by comparing the mating investment of males of different qualities and phenotypes to high‐ and low‐quality females. We used two datasets that together contained information from 60 empirical studies, comprising 52 species. We found that males of all qualities and phenotypes prefer high‐quality females, but differ in the strength of such preference. High‐ and medium‐quality males are choosier than low‐quality males. Similarly, males that are larger or in greater body condition are choosier than their counterparts. In contrast, male body mass and age are not associated with changes in male mate choice. We also show that experimental design may influence our understanding of male mating investment patterns, which may limit the generalisation of our findings. Nonetheless, we argue that male quality may be an important feature in the expression of male mate choice.

Diversity in warning coloration: selective paradox or the norm?

Aposematic theory has historically predicted that predators should select for warning signals to converge on a single form, as a result of frequency-dependent learning. However, widespread variation in warning signals is observed across closely related species, populations and, most problematically for evolutionary biologists, among individuals in the same population. Recent research has yielded an increased awareness of this diversity, challenging the paradigm of signal monomorphy in aposematic animals. Here we provide a comprehensive synthesis of these disparate lines of investigation, identifying within them three broad classes of explanation for variation in aposematic warning signals: genetic mechanisms, differences among predators and predator behaviour, and alternative selection pressures upon the signal. The mechanisms producing warning coloration are also important. Detailed studies of the genetic basis of warning signals in some species, most notably Heliconius butterflies, are beginning to shed light on the genetic architecture facilitating or limiting key processes such as the evolution and maintenance of polymorphisms, hybridisation, and speciation. Work on predator behaviour is changing our perception of the predator community as a single homogenous selective agent, emphasising the dynamic nature of predator-prey interactions. Predator variability in a range of factors (e.g. perceptual abilities, tolerance to chemical defences, and individual motivation), suggests that the role of predators is more complicated than previously appreciated. With complex selection regimes at work, polytypisms and polymorphisms may even occur in Müllerian mimicry systems. Meanwhile, phenotypes are often multifunctional, and thus subject to additional biotic and abiotic selection pressures. Some of these selective pressures, primarily sexual selection and thermoregulation, have received considerable attention, while others, such as disease risk and parental effects, offer promising avenues to explore. As well as reviewing the existing evidence from both empirical studies and theoretical modelling, we highlight hypotheses that could benefit from further investigation in aposematic species. Finally by collating known instances of variation in warning signals, we provide a valuable resource for understanding the taxonomic spread of diversity in aposematic signalling and with which to direct future research. A greater appreciation of the extent of variation in aposematic species, and of the selective pressures and constraints which contribute to this once-paradoxical phenomenon, yields a new perspective for the field of aposematic signalling.

Influence of food availability on mate-guarding behaviour of ladybirds

A recent study on ladybird, Menochilus sexmaculatus (Fabricius) demonstrates that males perform post-copulatory mate guarding in the form of prolonged mating durations. We investigated whether food resource fluctuation affects pre- and post-copulatory behaviour of M. sexmaculatus. It has not been studied before in ladybirds. For this, adults were subjected to prey resource fluctuations sequentially at three levels: post-emergence (Poe; 10 days), pre-mating (Prm; 24 h) and post-mating (Pom; 5 days; only female). The food resource conditions at each level could be any one of scarce, optimal or abundant. Pre-copulatory and post-copulatory behaviour, and reproductive output were assessed. Post-emergence and pre-mating nutrient conditions significantly influenced the pre-copulatory behaviour. Males reared on scarce post-emergence conditions were found to require significantly higher number of mating attempts to establish mating unlike males in the other two food conditions. Under scarce post-emergence and pre-mating conditions, time to commencement of mating and latent period were high but opposite result was obtained for mate-guarding duration. Fecundity and per cent egg viability were more influenced by post-mating conditions, with scarce conditions stopping oviposition regardless of pre-mating and post-emergence conditions. Present results indicate that pre- and post-copulatory behaviour of ladybird is plastic in nature in response to food resource fluctuations.

Toward Understanding the Repeated Occurrence of Associations between Melanin-Based Coloration and Multiple Phenotypes

Melanin is the most widespread pigment in organisms. Melanin-based coloration has been repeatedly observed to be associated with the same traits and in the same direction in different vertebrate and insect species. However, whether any factors that are common to different taxa account for the repeated evolution of melanin-phenotype associations remains unclear. We propose to approach this question from the perspective of convergent and parallel evolution to clarify to what extent different species have evolved the same associations owing to a shared genetic basis and being subjected to similar selective pressures. Our current understanding of the genetic basis of melanin-phenotype associations allows for both convergent and parallel evolution, but this understanding is still limited. Further research is needed to clarify the generality and interdependencies of the different proposed mechanisms (supergenes, pleiotropy based on hormones, or neural crest cells). The general ecological scenarios whereby melanin-based coloration is under selection-protection from ultraviolet radiation, thermoregulation in cold environments, or as a signal of social status-offer a good opportunity to study how melanin-phenotype associations evolve. Reviewing these scenarios shows that some traits associated with melanin-based coloration might be selected together with coloration by also favoring adaptation but that other associated traits might impede adaptation, which may be indicative of genetic constraints. We therefore encourage further research on the relative roles that selection and genetic constraints play in shaping multiple melanin-phenotype associations. Placed into a phylogenetic context, this will help clarify to what extent these associations result from convergent or parallel evolutionary processes and why melanin-phenotype associations are so common across the tree of life.

Mating experience influences mate choice and reproductive output in an aphidophagous ladybird, Menochilus sexmaculatus

Information about mating status can be used to decide about whether to invest resources in mating with a particular partner. In the present study, we evaluated mate choice in relation to the mating experience of males and females of Menochilus sexmaculatus. We subjected both unmated and multiply mated males and females to different mate choice trials. The mating experience of the adults includes unmated, once-mated, twice-mated and multiply mated. The mate choice trials revealed that unmated adults were preferred over mated adults by both unmated and multiply mated partners. This preference for unmated partners also had consequences for mating behaviour and reproductive output. Unmated and multiply mated females commenced mating with unmated males earlier. In addition, unmated and multiply mated males invested more time in copula with unmated females. Moreover, females mated with unmated males were more fecund than those mated with previously mated males. This suggests that mating experience of mates may influence mating and reproductive behaviour in this species.

Last male wins the egg fertilization fight: A case study in ladybird, Menochilus sexmaculatus

Sexual selection and the mechanisms involved in sperm competition have not been greatly explored in ladybird beetles. The present study was conducted to investigate the processes of sperm competition and the role of mate guarding behaviour in its regulation in ladybird beetles. We investigated these questions in polyandrous females of the ladybird, Menochilus sexmaculatus (Coleoptera: Coccinellidae) using a phenotypic marker (typical and intermediate morph) to assess paternity of offspring; to determine sperm competition. We conducted two double mating experiments: (i) complete first and second matings, and (ii) disrupted first and complete second matings each using homomorphic and heteromorphic pairing in alternation. Males which mated last were found to sire up to 72% of the offspring produced, indicating last male sperm precedence. Morph itself, independent of mating order, did not have a significant effect on proportion of offspring sired. Paternity share of the last male was negatively associated with mating duration of the first male; mating duration of the first male being indicative of mate guarding. This therefore indicates that prolonged matings by first males are essentially examples of post-copulatory mate guarding to prevent last male sperm precedence.

Influence of temperature on reproductive biology and phenotype of a ladybird, Menochilus sexmaculatus (Fabricius) (Coleoptera: Coccinellidae)

Body melanisation in insects is polygenic, resulting from genetic polymorphism or phenotypic plasticity, with diverse implications ranging from thermal budgeting to reproductive success. In this study, we assessed the, mate choice, reproductive success, and offspring colouration of typical (T) and melanic (M) morphs of the ladybird Menochilus sexmaculatus paired at three temperatures 15°C, 25°C and 35°C. Mating success of the two morphs and the consequences for offspring fitness and offspring phenotype under these temperature regimes were evaluated. Melanic adults of both sexes achieved significantly higher mating success at 15°C and 25°C, but at 35°C no influence of adult morph on mate selection was observed. Melanic females were more fecund than typical females at all temperatures. Offspring of melanic parents developed faster than those of typicals at 15°C and 25°C, but not at 35°C. Evidence was also found of phenotypic plasticity in colour form at 15°C and 35°C. At 25°C the parents of pure (T) and (M) morphs produced offspring of the same morph. However, low temperature induced partial melanisation among the offspring of typical parents (T). Whereas at 35°C the offspring of (T) parents became paler in colour with very fine zigzag lines on elytra, i.e. they decrease the degree of melanisation. Pure melanics (M) compensated for elevated temperature stress by producing offspring that were either pure melanic but small or large with reduced melanisation. Our results on offspring phenotype variation indicate that the degree of melanism in morphs is a result of environmentally regulated expression of the parental genotype.