The model organism Drosophila melanogaster has become a focal system for investigations of rapidly evolving genital morphology as well as the development and functions of insect reproductive structures. To follow up on a previous paper outlining unifying terminology for the structures of the male terminalia in this species, we offer here a detailed description of the female terminalia of D. melanogaster . Informative diagrams and micrographs are presented to provide a comprehensive overview of the external and internal reproductive structures of females. We propose a collection of terms and definitions to standardize the terminology associated with the female terminalia in D. melanogaster and we provide a correspondence table with the terms previously used. Unifying terminology for both males and females in this species will help to facilitate communication between various disciplines, as well as aid in synthesizing research across publications within a discipline that has historically focused principally on male features. Our efforts to refine and standardize the terminology should expand the utility of this important model system for addressing questions related to the development and evolution of animal genitalia, and morphology in general.

Rapid divergence in genital structures among nascent species has been posited to be an early‐evolving cause of reproductive isolation, although evidence supporting this idea as a widespread phenomenon remains mixed. Using a collection of interspecific introgression lines between two Drosophila species that diverged approximately 240,000 years ago, we tested the hypothesis that even modest divergence in genital morphology can result in substantial fitness losses. We studied the reproductive consequences of variation in the male epandrial posterior lobes between Drosophila mauritiana and Drosophila sechellia and found that divergence in posterior lobe morphology has significant fitness costs on several prefertilization and postcopulatory reproductive measures. Males with divergent posterior lobe morphology also significantly reduced the life span of their mates. Interestingly, one of the consequences of genital divergence was decreased oviposition and fertilization, which suggests that a sensory bias for posterior lobe morphology could exist in females, and thus, posterior lobe morphology may be the target of cryptic female choice in these species. Our results provide evidence that divergence in genitalia can in fact give rise to substantial reproductive isolation early during species divergence, and they also reveal novel reproductive functions of the external male genitalia in Drosophila.

The marine environment of the Persian Gulf is characterized by extreme biophysical factors, like high salinities. This gulf is a semi-enclosed basin and is connected to the Gulf of Oman via the narrow Strait of Hormuz that may act as a barrier to gene flow between the two gulfs. Consequently, animal populations living in the Persian Gulf are hypothesized to be isolated and thus to evolve independently from neighbouring populations. We tested this hypothesis with the xanthid crab, Leptodius exaratus (H. Milne Edwards, 1834), which is one of the most common intertidal crabs occurring in the Persian Gulf and the Gulf of Oman. Four-hundred-and-fifty specimens were collected from eight sampling sites, i.e., four sites each in the Persian Gulf and the Gulf of Oman. Fifteen morphometric characters were measured. Males and females were analysed separately to avoid bias as a consequence of sexual dimorphism. Due to the lack of normal distribution in males, two different approaches were carried out in this paper. Female specimens were included in parametric analyses, while males were tested with permutational multivariate analyses of variance. In female morphometric characters, t-test analyses showed significant differences between the two sets of populations, and the discriminant analysis showed divergence between the two groups (with 83% correct groupings). In the males, the applied analyses showed a significant difference (P = 0.002) between the two gulfs. These divergences can be interpreted as a consequence of regional adaptations and a low rate of larval migration between the two gulfs. ZUSAMMENFASSUNGDer marine Lebensraum des Persischen Golfs zeichnet sich durch extreme biophysikalische Faktoren, wie hohe Salinitäten, aus. Dieser Golf ist ein fast durchgehend abgetrenntes Meeresbecken und ist mit dem benachbarten Golf von Oman nur durch die schmale Straße von Hormus verbunden, die als Genflussbarriere zwischen den beiden Becken wirken könnte. Entsprechend wird vermutet, dass Populationen von Meerestieren im Persischen Golf isoliert sind und unabhängig von

22Rapid divergence in genital structures among nascent species has been posited to be an early-23 evolving cause of reproductive isolation, although evidence supporting this idea as a widespread 24 phenomenon remains mixed. Using a collection of interspecific introgression lines between two 25Drosophila species that diverged ~240,000 years ago, we tested the hypothesis that even modest 26 divergence in genital morphology can result in substantial fitness losses. We studied the 27 reproductive consequences of variation in the male epandrial posterior lobes between Drosophila 28 mauritiana and D. sechellia and found that divergence in posterior lobe morphology has 29 significant fitness costs on several pre-fertilization and post-copulatory reproductive measures. 30Males with divergent posterior lobe morphology also significantly reduced the life span of their 31 mates. Interestingly, one of the consequences of genital divergence was decreased oviposition 32 and fertilization, which suggests that a sensory bias for posterior lobe morphology could exist in 33 females, and thus posterior lobe morphology may be the target of cryptic female choice in these 34 species. Our results provide evidence that divergence in genitalia can in fact give rise to 35 substantial reproductive isolation early during species divergence, and they also reveal novel 36 reproductive functions of the external male genitalia in Drosophila. 37 38 39 40 41 42 Prum 2015), the importance of divergence in genital morphology as a cause of RI has been 56 debated (Shapiro and Porter 1989; Masly 2012). 57 Nonetheless, several recent studies in a variety of taxa support the idea that 58 morphological divergence in external genitalia can indeed cause RI early during the speciation 59 process via both mechanical and sensory incompatibilities. One well-characterized example of 60 mechanical incompatibility between male and female genitalia occurs among several species of 61 Carabus (subgenus Ohomopterous) ground beetles, where species divergence in male aedeagus 62 morphology causes substantial damage to the female vaginal appendix during copulation, 63 resulting in reduced reproductive output, damage to the aedeagus, and even female mortality 64 (Sota and Kubota 1998; Nagata et al. 2007; Sota and Tanabe 2010; Kyogoku and Sota 2015). 65 of species divergence. Our test takes advantage of several D. mauritiana-D. sechellia genetic 106 introgression lines that possess small chromosomal segments (~1.5 Mb on average) of the D. 107 mauritiana genome within a predominantly D. sechellia white (w) genomic background (Masly 108 and Presgraves 2007). Pure species D. mauritiana possesses small finger-shaped PLs, whereas 109 D. sechellia possesses much larger goose-headed-shaped PLs, with a long neck and characteristic 110 "beak." Several of these D. mauritiana-D. sechellia introgression lines possess interspecific 111 6 variation in male PL morphology including transgressive variation in PL size, whereas others 112 possess morphology that is similar to D. sechellia w...

The model organism Drosophila melanogaster has become a focal system for investigations of rapidly evolving genital morphology as well as the development and functions of insect reproductive structures. To follow up on a previous paper outlining unifying terminology for the structures of the male terminalia in this species, we offer here a detailed description of the female terminalia of D. melanogaster. Informative diagrams and micrographs are presented to provide a comprehensive overview of the external and internal reproductive structures of females. We propose a collection of terms and definitions to standardize the terminology associated with the female terminalia in D. melanogaster and we provide a correspondence table with the terms previously used. Unifying terminology for both males and females in this species will help to facilitate communication between various disciplines, as well as aid in synthesizing research across publications within a discipline that has historically focused principally on male features. Our efforts to refine and standardize the terminology should expand the utility of this important model system for addressing questions related to the development and evolution of animal genitalia, and morphology in general.