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Sexual selection influences both genital diversity and mating behaviors, yet the integrated coevolution of pre- (behavioral) and postcopulatory (anatomical) traits in both sexes has received little attention. Traits could potentially evolve through an arms race model of escalations in male persistence and female resistance, and/or through a tradeoff model of inverse correlations between investments in pre- and postcopulatory traits. Pre- and postcopulatory traits of dusky dolphins (Lagenorhynchus obscurus) were compared with bottlenose dolphins (Tursiops spp.) and harbor porpoises (Phocoena phocoena). Relative testes size and vaginal complexity were measured from dissected specimens. Behavioral traits were analyzed from video recordings of individuals in free-ranging populations. Female precopulatory and male postcopulatory traits were associated, whereas female and male postcopulatory traits or female pre- and postcopulatory traits were not associated. Dusky dolphins differed substantially in several behavioral traits including longer durations of mating group interactions, lower rates of copulation attempts, more males per group, and higher female behavioral resistance. To explore complex processes of integrative coevolution, we recommend future research incorporate pre- and postcopulatory traits and focus on alternative measures of female resistance and male persistence.

Few studies have examined the natural complex pigmentation patterns of whitebeaked dolphins. From 2002 to 2014, whale-watching trips in Iceland provided a platform of opportunity to collect a large body of photographs of free-ranging individuals from a single area of distribution for this species. Based on 823 images, 571 individuals showing one or more color components were identified, and assigned to the following four age classes: adults (n = 437), juveniles (n = 109), calves (n = 14), and neonates (n = 11). A total of 26 color components were observed and described: seven terms previously applied to white-beaked dolphins, 12 previously applied to other dolphin species, and seven newly defined terms. Results showed that each age class could be positively identified by differences in specific color components, some of which were exclusive. Therefore, color patterns may prove useful in estimating maturity in free-ranging white-beaked dolphins. This tool could be further refined through assessment of a wide sample of freshly stranded specimens of known sex and age, which could reveal new age class-specific components, as well as sexually dimorphic characteristics not seen here. Geographic variation should be investigated by comparing image data sets and stranded animals from different parts of the North Atlantic.

Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Phocoena phocoena). Males attempt copulation by approaching a female exclusively on her left side. to understand if this unusual lateralized behavior may have coevolved with genital morphology, we quantified the shape of female and male harbor porpoise reproductive tracts using 2D geometric morphometrics and 3D models of the vaginal lumen and inflated distal penis. We found that the vaginas varied individually in shape and that the vaginas demonstrated both significant directional and fluctuating asymmetry. This asymmetry resulted from complex 3D spirals and vaginal folds with deep recesses, which may curtail the depth or direction of penile penetration and/or semen movement. the asymmetric shapes of the vaginal lumen and penis tip were both left-canted with similar angular bends that mirrored one another and correspond with the left lateral mating approach. We suggest that the reproductive anatomy of both sexes and their lateral mating behavior coevolved. Left-or right-bias in morphology and behavior in otherwise bilaterally symmetrical animals manifests in diverse biological phenomena such as mating, foraging, predation, predator defense, and communication 1,2. Asymmetries in genital morphology are known in several animal taxa 3-5 , and although lateralization in courtship behavior is found across animal taxa 6 , it was unknown in mammals until recently 7. While some morphological and behavioral asymmetries related to mating have been identified, the relationship between genital asymmetry and lateralized mating behaviors, as well as their evolutionary significance, has rarely been examined. Questions remain about how asymmetry in one sex influences the behavior or morphology of the other sex and whether asymmetries arise from adaptive (directional evolution) or non-adaptive (genetic drift) mechanisms. Instances in which one or both sexes have asymmetries in both mating behavior and genitalia may be more common than is currently recognized. For example, lateralized mating behavior occurs in male poeciliid fish, which angle their gonodopodium (intromittent organ) to either the left or right side and are restricted to mating with females that have a genital opening on the same side 8-10. Similarly, male tree swallows tend to copulate from the left, perhaps because the female's one active oviduct is on the left side 11. Male earwigs with paired penises preferentially use their right penis during copulation, which may be driven by female genital morphology 12. Male and female waterfowl have asymmetric genitalia that spiral in opposite directions and females have evolved behavioral strategies to influence control over insemination 13-15. However, mating behaviors are not later...