Laura S. Corley

Highly variable sperm precedence in the stalk-eyed fly, Teleopsis dalmanni

BackgroundWhen females mate with different males, competition for fertilizations occurs after insemination. Such sperm competition is usually summarized at the level of the population or species by the parameter, P2, defined as the proportion of offspring sired by the second male in double mating trials. However, considerable variation in P2 may occur within populations, and such variation limits the utility of population-wide or species P2 estimates as descriptors of sperm usage. To fully understand the causes and consequences of sperm competition requires estimates of not only mean P2, but also intra-specific variation in P2. Here we investigate within-population quantitative variation in P2 using a controlled mating experiment and microsatellite profiling of progeny in the multiply mating stalk-eyed fly, Teleopsis dalmanni.ResultsWe genotyped 381 offspring from 22 dam-sire pair families at four microsatellite loci. The mean population-wide P2 value of 0.40 was not significantly different from that expected under random sperm mixing (i.e. P2 = 0.5). However, patterns of paternity were highly variable between individual families; almost half of families displayed extreme second male biases resulting in zero or complete paternity, whereas only about one third of families had P2 values of 0.5, the remainder had significant, but moderate, paternity skew.ConclusionOur data suggest that all modes of ejaculate competition, from extreme sperm precedence to complete sperm mixing, occur in T. dalmanni. Thus the population mean P2 value does not reflect the high underlying variance in familial P2. We discuss some of the potential causes and consequences of post-copulatory sexual selection in this important model species.

Intrinsic, inter‐specific competition between egg, egg–larval, and larval parasitoids of plusiine loopers

Abstract 1. Intrinsic, inter‐specific competition between parasitoid wasp species is a key factor in ecological community dynamics and is particularly important for application in biological control. Here three parasitoid wasp species with overlapping host ranges and differing life history strategies were chosen to examine parasitoid–parasitoid interactions: the egg parasitoid Trichogramma pretiosum, the egg–larval, polyembryonic parasitoid wasp Copidosoma floridanum, and the gregarious larval parasitoid Glyptapanteles pallipes, with the plusiine loopers Acanthoplusia agnata and Trichoplusia ni as hosts.

Both endogenous and environmental factors affect embryo proliferation in the polyembryonic wasp Copidosoma floridanum

Summary Copidosoma floridanum is a polyembryonic, parasitic wasp of the moth Trichoplusia ni. Following oviposition into a host, the C. floridanum egg initially undergoes complete (holoblastic) cleavage to form a single morula stage embryo. This embryo then undergoes a proliferation phase in which multiple, secondary morulae develop. C. floridanum has also evolved a caste system whereby some secondary morulae develop into soldier larvae whose function is defense whereas others develop into reproductive larvae that become adult wasps. In the current study, we conducted manipulative and candidate gene studies to identify factors affecting the proliferation phase of C. floridanum development. Transplantation of morulae of different ages into different host stages indicated that both embryo age and host environment affected the total number of offspring produced per morula. Morula age and brood size also significantly affected whether offspring of one or both castes were produced in a brood. In contrast, the host environment did not significantly affect caste formation. A putative homolog of the gene hedgehog (Cf‐hh) was partially cloned from C. floridanum. In situ hybridization studies indicated that Cf‐hh was expressed in secondary morulae during the proliferation phase of development, suggesting a possible role for the Hh signaling pathway in the evolution of polyembryony.

Microevolution and development: studies of the genetic basis of adaptive variation in insects

Animals have the ability to adapt to their environments in remarkable and diverse ways via changes in their phenotypes, including both behavioral and morphological variation. The renaissance of evolutionary developmental biology has largely come from the traditions of developmental genetics and as such has focused largely on qualitative phenotypic changes through evolution (Raff 1996; Carroll et al. 2001). However, understanding the evolution of the genotype–phenotype map from the perspective of intraspecific variation may actually allow a more complete explanation of adaptive phenotypic change. The relatively new and exciting area of microevodevo combines the study of phenotypic variation with developmental genetics to provide the genetic mechanisms by which an animal evolves (Palopoli and Patel 1996; Gerhart and Kirschner 1997; Tautz and Schmidt 1998; West-Eberhard 1998, 2003; Goodman and Coughlin 2000; Evans and Wheeler 2001; Johnson and Porter 2001; Corley 2002; Haag 2002; Brakefield et al. 2003; Purugganan and Gibson 2003; Rutherford 2003). Evo-devo studies are beginning to fill in the ‘‘black box’’ that has traditionally existed between an animal’s genotype and phenotype (Gibson 1999; Emlen and Nijhout 2000; Beldade et al. 2002; Brakefield et al. 2003). Most research in evo-devo has focused on comparisons of highly conserved genes chosen because they are already known to be involved in the development of homologous traits in a model organism such as the fruit fly, Drosophila melanogaster, or the laboratory mouse, Mus musculus (Haag and True 2001). However, with the onset of powerful new biotechnologies such as microarray analyses and comparative genomics, it is now possible to add to our understanding of the genetic basis for adaptive evolution by studying nonmodel organisms (Bochner 2003; Purugganan and Gibson 2003; Scharf et al. 2003). Although the articles in this issue do not discuss isopods specifically, we are ‘‘singing a song of six legs’’ as Garstang so joyfully put it. The papers in this special issue are a collection from the symposium titled ‘‘Understanding microevolution & development in the arthropods’’ in the Evolution & Genetics Section at the XXII International Congress of Entomology that was held in Brisbane, Australia in August 2004. This symposium united researchers investigating the proximate developmental genetic mechanisms underlying complex phenotypes in insects. The goals of this special section are to present the most recent advances and methodologies that are available for the study of the genetic basis of adaptive variation and to discuss how to take advantage of the amazing pool of morphological, physiological, and life history diversity found in the arthropods. The contributors include scientists who integrate developmental biology, evolutionary biology, and ecology, and thus employ multidisciplinary approaches to the study of microevolution and development. Moreover, these participants represent some of the most promising scientists in the field of developmental evolutionary biology. Given the sharp focus of the symposium and the diversity of participants, the primary goal of the symposium was to spark a synthesis of ideas about microevolution and development, which will diffuse rapidly throughout the scientific community.