Publisher Summary
The mechanisms of sexual reproduction are expected to be complex and evolutionarily dynamic in internally fertilizing species, where numerous biochemical, physiological, morphological, and behavioral mechanisms mediate insemination, sperm migration, sperm storage, the maintenance of sperm viability, and sperm modification, all of which must be properly executed before fertilization can begin. This situation provides the opportunity for postcopulatory sexual selection, which is predicted to further enhance complexity and diversification in genes contributing to differential male fertilization success and female control over paternity. It is becoming increasingly clear that sperm and ejaculate constituents evolve in response to selection pressures imposed by the female reproductive tract. Ejaculate–female interactions (EFIs) can determine whether or not a reproductive attempt is successful and can influence the outcome of sperm competition within populations. Evolutionary diversification of EFIs may further determine the extent of reproductive isolation and gene introgression between closely related species. This chapter aims to illustrate the pervasiveness of EFIs by discussing different types and what is known about their underlying mechanisms, and it considers the evolutionary significance of EFIs. Furthermore the chapter reviews evidence for rapid evolutionary diversification of EFI genes, correlated evolution of sex-specific EFI traits, and the relationship between genetic compatibility, male–female interactions, and patterns of sperm precedence.

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Ejaculate–female and sperm–female interactions

Regulation of sexual receptivity of female Mediterranean fruit flies: old hypotheses revisited and a new synthesis proposed

The insect spermatheca: an overview.

A light and electron microscopical study of the spermathecae and ventral receptacle of Anastrepha suspensa (Diptera: Tephritidae) and implications in female influence of sperm storage.

The species-specificity of male genitalia has been well documented in many insect groups and sexual selection has been proposed as the evolutionary force driving the often rapid, morphological divergence. The internal female genitalia, in sharp contrast, remain poorly studied. Here, we present the first comparative study of the internal reproductive system of Sepsidae. We test the species-specificity of the female genitalia by comparing recently diverged sister taxa. We also compare the rate of change in female morphological characters with the rate of fast-evolving, molecular and behavioral characters. We describe the ectodermal parts of the female reproductive tract for 41 species representing 21 of the 37 described genera and define 19 morphological characters with discontinuous variation found in eight structures that are part of the reproductive tract. Using a well-resolved molecular phylogeny based on 10 genes, we reconstruct the evolution of these characters across the family [120 steps; Consistency Index (CI): 0.41]. Two structures, in particular, evolve faster than the rest. The first is the ventral receptacle, which is a secondary sperm storage organ. It accounts for more than half of all the evolutionary changes observed (7 characters; 61 steps; CI: 0.46). It is morphologically diverse across genera, can be bi-lobed or multi-chambered (up to 80 chambers), and is strongly sclerotized in one clade. The second structure is the dorsal sclerite, which is present in all sepsids except Orygma luctuosum and Ortalischema albitarse. It is associated with the opening of the spermathecal ducts and is often distinct even among sister species (4 characters; 16 steps; CI: 0.56). We find the internal female genitalia are diverse in Sepsidae and diagnostic for all species. In particular, fast-evolving structures like the ventral receptacle and dorsal sclerite are likely involved in post-copulatory sexual selection. In comparison to behavioral and molecular data, the female structures are evolving 2/3 as fast as the non-constant third positions of the COI barcoding gene. They display less convergent evolution in characters (CI = 0.54) than the third positions or sepsid mating behavior (CI
 COI
 = 0.36; CIBEHAV = 0.45).

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Unlocking the "Black box": internal female genitalia in Sepsidae (Diptera) evolve fast and are species-specific

The association between the ventral nervous system and the sperm storage organs in Anastrepha suspensa Loew was examined to elucidate possible mechanisms that may influence sperm transport in the female reproductive tract. Such mechanisms are of importance with respect to the sexual conflict over paternity. A single, abdominal ganglion is present under the first abdominal sternite of A. suspensa. The ganglion is ovoid (L = 280 ± 18 μm ±SD, W = 230 ± 15 μm ±SD) and has a large nerve fiber extending anteriorly to the thoracico-abdominal ganglion and a large, branched nerve fiber extending posteriorly to the reproductive system. The presence of an abdominal ganglion is atypical for the Cyclorrapha flies and its position in the abdomen is atypical for the Insecta. The ganglion's position suggests that in some taxa the evolutionary trend toward fewer abdominal ganglia has occurred with the concomitant displacement of caudal ganglia to more anterior positions in the abdomen. Nerves extending from this ganglion synapse with muscle fibers at the base of the spermathecae and the surface of the unicellular gland cells surrounding the spermathecal capsule. When stained with HRP Ab, synaptic boutons are also visible along the length of the spermathecal ducts in association with the longitudinal muscle fibers and on the muscle fibers surrounding the ventral receptacle. These findings suggest that females have the potential to affect sperm transport in their reproductive tract.

Ann H. Fritz

Papers

A light and electron microscopical study of the spermathecae and ventral receptacle of Anastrepha suspensa (Diptera: Tephritidae) and implications in female influence of sperm storage.

A Single, Abdominal Ganglion in Anastrepha suspensa (Diptera: Tephritidae) and Its Innervation of the Female Sperm Storage Organs