Parasite Load, Body Size, And Age Of Wild‐Caught Male Field Crickets (Orthoptera: Gryllidae): Effects On Sexual Selection

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137421/1/evo02515.pd

The effects of gregarine parasites, body size, and time of day on spermatophore production and sexual selection in field crickets

In laboratory experiments measuring the rate of spermatophore production in the field crickets Gryllus veletis and G. pennsylvanicus by confining single males with a conspecific female, 0–10 spermatophores were produced by each male within 24 h. The number of spermatophores produced was unrelated to a male's body size, but was significantly negatively correlated with the natural levels of gregarines, a protozoan gut parasite, in the males. Spermatophore production in the laboratory peaked between 0600 and 1000 h, as did the proportion of courtship songs given by male crickets in the field, suggesting that mating may occur more frequently in the morning. When single males were placed in jars with two conspecific females, 49% transferred spermatophores to both females, whereas 51% of males only gave spermatophores to one of the females. The results support the hypothesis that parasites are important in sexual selection, and are used to propose a new interpretation of post-copulatory guarding in crickets.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46882/1/265_2004_Article_BF00324437.pd

Sex differences in metabolic rates in field crickets and their dipteran parasitoids

Sex differences in metabolic rate (MR) can result from dimorphism in the performance of energetically demanding activities. Male crickets (Teleogryllus oceanicus) engage in costly calling and aggressive activity not performed by females. Consistent with this difference, we found higher maximal MR, factorial scope, and fat content in males than females. T. oceanicus song is also costly because it attracts the parasitoid fly Ormia ochracea. Parasitized crickets had reduced maximal MR consistent with a metabolic cost to harboring larvae. This cost was greater for females, either because females invest more heavily into reproduction at the expense of metabolic capacity, or because males are under stronger selection to respond to infection. Little is known about O. ochracea outside of its auditory system and parasitic lifestyle. We observed greater resting MR in male flies, possibly reflecting a sex difference in the requirement for metabolic power output, because male flies perform potentially costly mating behavior not seen in females. We found a positive relationship between larval density within a cricket and pupal resting MR, suggesting that crickets in good condition are able to both harbor more larvae and produce larvae with higher resting MR. These results reveal a complex interplay between the metabolism of crickets and their fly parasitoids

Effects of relaxed selection on female response to male song in crickets (Acheta domesticus)

Selection acts differently on animals in captivity compared to those in natural conditions. As a result, individuals bred in captivity for many generations may exhibit traits that greatly differ from their wild counterparts. We decided to use The Common House Cricket, Acheta domesticus, as our study species because they are found feral in most of the United States and have also been extensively bred for live pet food. As such, they are ideal candidates to observe the effects of relaxed selection. Male crickets produce a song to attract females. In the overcrowded conditions of captivity, there is much less selective pressure for females to be responsive to male song. Therefore, we hypothesize that captive female individuals are less sensitive to sound and so will respond more slowly to male song.This research was supported by the Undergraduate Research Opportunities Program (UROP)

Sex Differences in Susceptibility to Infection: An Evolutionary Perspective

Abstract Patterns of sex differences in parasite infection and immune responses have been noted for many decades. Although numerous explanations for such differences have been proposed, including hormonal patterns and sex-biased exposure to infective stages of pathogens, these have largely been proximate explanations that address the mechanisms immediately responsible for the findings but do not take a more integrative or ultimate approach. Here, we present an evolutionary framework for understanding the origin and maintenance of sex differences in the incidence and susceptibility to infectious disease, using life history theory and sexual selection to make predictions about when males or females in a particular species are expected to be more or less susceptible to parasites

Molecular biogeography and host relations of a parasitoid fly

© 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. Successful geographic range expansion by parasites and parasitoids may also require host range expansion. Thus, the evolutionary advantages of host specialization may trade off against the ability to exploit new host species encountered in new geographic regions. Here, we use molecular techniques and confirmed host records to examine biogeography, population divergence, and host flexibility of the parasitoid fly, Ormia ochracea (Bigot). Gravid females of this fly find their cricket hosts acoustically by eavesdropping on male cricket calling songs; these songs vary greatly among the known host species of crickets. Using both nuclear and mitochondrial genetic markers, we (a) describe the geographical distribution and subdivision of genetic variation in O. ochracea from across the continental United States, the Mexican states of Sonora and Oaxaca, and populations introduced to Hawaii; (b) demonstrate that the distribution of genetic variation among fly populations is consistent with a single widespread species with regional host specialization, rather than locally differentiated cryptic species; (c) identify the more-probable source populations for the flies introduced to the Hawaiian islands; (d) examine genetic variation and substructure within Hawaii; (e) show that among-population geographic, genetic, and host song distances are all correlated; and (f) discuss specialization and lability in host-finding behavior in light of the diversity of cricket songs serving as host cues in different geographically separate populations