Male larval experience of cues from adult rivals alters lifetime sperm investment patterns in a sperm heteromorphic moth, Ephestia kuehniella

Male animals may adjust their resource allocations for reproduction and other fitness functions in response to cues from rivals. For instance, adult males increase their investment in sperm for a higher paternity share when they perceive sperm competition risk in their surroundings. In nature, both juveniles and adults may coexist spatially and temporally. Yet, it is not clear how juvenile males of different ages respond to cues from adult rivals and fine-tune their lifetime investment in sperm production and ejaculation in any insect. Here we used the Mediterranean flour moth, Ephestia kuehniella, which produces both fertile eupyrene and infertile apyrene sperm, to explore this question. We demonstrate that the late, but not early, instar larvae are sensitive to adult male cues. As a response, they produce more sperm before emergence and their resultant adults have shorter mating latency and ejaculate more sperm in the first few matings. When the juvenile stage produces more eupyrenes, the adult stops making these sperm, but regardless of the number of apyrenes produced during the juvenile stage, the adult continues to make them. These findings suggest that the number of spermatogonia for eupyrenes may be limited and that for apyrenes may be flexible. Our results show that the insect does not trade off survival, mating frequency, body size, or testis size for sperm production in response to adult males during the larval stage. Knowledge created in the present study offers insight into the stage-dependent sensitivity of juvenile males to cues from adult rivals and subsequent lifetime resource allocations.

Local mate competition model alone cannot predict the offspring sex ratio in large and dense populations of a haplodiploid arthropod

Sex ratio in animals has profound impacts on the fitness of mothers and their offspring.When the local competition intensity is sex-specific,selection favors the sex that may mitigate such negative impacts(West 2009).This may occur under 1)local mate competition(LMC)-in a discrete population established by one or a few foundresses,they tend to produce female-biased offspring sex ratio to reduce the LMC between related males(Hamilton 1967);2)local resource competition(LRC)-in a dense population where related individuals compete for resources,mothers are selected to produce more off spring of dispersive sex to decrease resource competition(Clark 1978;Wild and Taylor 2004;Iritani et al.2021),and 3)local resource enhancement(LRE)-when one sex helps one another rather than compete with one another,selection favors an excess production of the more helpful sex(Taylor 1981).

Conspecific cues mediate habitat selection and reproductive performance in a haplodiploid spider mite

Selection of a suitable habitat by animals before settlement is critical for their survival and reproduction.In silk-spinning arthropods like spider mites,denser webs offer protection from predation and serve as a dispersal mode.Settling in habitats with the presence of conspecifics and silk webs can benefit the habitat-searching females.Silk and conspecifics usually coexist,but their distinct effects on female colonization have received little attention.In this study,we used a haplodiploid spider mite,Tetranychus ludeni Zacher(Acari:Tetranychidae),to examine the impact of conspecific cues,including cues from ovipositing conspecifics and silk,on habitat selection and subsequent reproductive performance of females.Results show that females significantly preferred habitats with cues from neighboring conspecifics and silk and neighboring conspecifics induced additive effect to that of silk on habitat selection.Conspecific cues did not boost female reproduction but facilitated females laying larger eggs that were more likely to be fertilized and to develop into daughters.When given a choice between silk-covered and clean habitats,females preferred silk-covered habitats,laid a similar number of eggs with similar size,but produced more daughters,suggesting that T.ludeni females can adjust the size threshold for fertilization in response to the current social environment.Knowledge of this study improves our understanding of spider mite habitat selection and post-settlement reproductive performance behaviors.