Size-dependent Mating Behaviours of Male Sand-bubbler Crab, Scopimera globosa: Alternative Tactics in the Life History

Male reproductive strategies in two species of spider crabs, Leurocyclus tuberculosus and Libinia spinosa

Reproductive strategies vary according to season length, individual reproductive traits, and factors associated with the social context such as density and sex ratio of the individuals. The social context predicts the intensity of sexual selection due to its effect on mate choice and intra-sexual competition. Moreover, it exacerbates the costs derived from sexual conflict and allows for the existence of alternative reproductive tactics to counteract such costs. However, these mechanisms are still underexplored in many animal taxa. Majoidea "spider crabs" show a diversity of life history, and behavioral and morphological adaptations for reproduction, which have evolved as an outcome of competition to maximize reproductive success. We aimed to analyze in this study, male reproductive strategies through mating behavior under different social contexts, density of individuals, and males size differences in two species of "spider crabs", Leurocyclus tuberculosus and Libinia spinosa. The experiments were as follows: one female and one male per aquarium (Experiment 1); a female and three males of similar sizes per aquarium (Experiment 2); and a female and three males of distinct sizes per aquarium (Experiment 3). The experiments showed that mating behavior and duration of mate guarding differ between species and among different social contexts. The presence of males with similar or different sizes showed a relevant different behavior, the female copulated with more than one male when males were similar in size (E2), and copulated only with the largest male when males were different in size (E3). In mate guarding, the shape and the use of the chelipeds had an important role: the male of Leurocyclus tuberculosus grasped the female with the chelipeds and did not fight with other males, but the male of Libinia spinosa surrounded the female with the chelipeds and fought with other males. The longest duration of mate guarding was during precopulatory guarding. Precopulatory guarding was present in all the experiments and its duration did not present significant differences among the experiments. However, in both species, the experiments differ in the duration of postcopulatory guarding until spawning. Gonopod morphology revealed important differences between species and are probably associated with sperm competition. The experiments under distinct social contexts linked to the use and shape of the chelipeds and the morphology of the gonopods, could allow to understand the functional significance of the different reproductive strategies.

Demographics of injuries indicate sexual coercion in a population of Painted Turtles (Chrysemyspicta)

Sexually coercive reproductive tactics are widespread among animals. Males may employ specialized structures to harass, intimidate, or physically harm females to force copulation, and injuries to the head and neck are reported in taxa with sexually coercive mating systems. The mating tactics of Painted Turtles (Chrysemys picta (Schneider, 1783)) are typically described as involving male courtship and female choice. In contrast, female Painted Turtles in our study population display injuries on the head and neck indicative of bite wounds inflicted by sexually dimorphic tomiodonts and weaponized shell morphology of males during reproductive interactions. Using a 24-year data set, we demonstrate population-level trends in soft tissue wounds inflicted by conspecifics. Adult females experienced more wounding than adult males or juveniles, and larger females had a greater probability of wounding than smaller females. Wounding was concentrated on the dorsal head and neck of females, consistent with expectation of sexual coercion. Furthermore, elevated rates of fresh wounding occurred during late summer, concurrent with the breeding period. By assessing wound demographics, we provide indirect evidence that the tomiodonts and shell of male Painted Turtles inflict injury and function as sexual weapons. These findings shed new light on our understanding of mating system complexity in an often-overlooked and difficult-to-observe taxonomic group.

Underground mating in the fiddler crab Uca tetragonon: the association between female life history traits and male mating tactics

Brood size and other life-history traits of females affect male investment in mating. Female Uca tetragonon, producing relatively small broods, were attracted to the burrows of males for underground mating (UM) while carrying eggs. Most UM females released larvae and ovulated new broods during the pairing, averaging 3.9 days. While a female was incubating one brood, another brood was developing within the ovaries because the females were feeding adequately during incubation. These findings suggest that in U. tetragonon, a small-brood species, females increase the total number of broods produced by breeding continually. In contrast, in large-brood species, feeding by ovigerous females is relatively brief and not enough to prepare the next brood during incubation, inducing temporal separation between incubation and brood production. Unlike females in other ocypodids where females with large broods remain in the breeding burrows of males, most female U. tetragonon left the male after UM. Wandering in female U. tetragonon after the pairs separate may occur because their small broods are adequately protected by an abdominal flap. Relative brood size probably determines the vulnerability of the incubated broods to the females' surface behavior. Hence, male reproductive success in large-brood species may decrease greatly if males expel their mates after ovulation, although this is not necessarily so in small-brood species. Whether the male drives away the female or not may depend on which behavior within either small- or large-brood species yields the greater male reproductive success. In U. tetragonon some females extruded eggs in their own burrows after surface mating as well as in males' burrows after UM. It was unclear whether females chose a male with a larger burrow as an UM mate unlike several large-brood species. Burrows of both UM males and ovigerous females in U. tetragonon were relatively smaller than those in some large-brood species, indicating that incubation of small broods does not require large burrows. Rather than benefits of UM by female choice, wandering resulting from intersexual conflict, and sperm competition may explain why some females mate in males' burrows in this small-brood species.