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Comparisons of 3D shapes have recently been applied to diverse anatomical structures using landmarking techniques. However, discerning evolutionary patterns can be challenging for structures lacking homologous landmarks. We used alpha shape analyses to quantify vaginal shape complexity in 40 marine mammal specimens including cetaceans, pinnipeds, and sirenians. We explored phylogenetic signal and the potential roles of natural and sexual selection on vaginal shape evolution. Complexity scores were consistent with qualitative observations. Cetaceans had a broad range of alpha complexities, while pinnipeds were comparatively simple and sirenians were complex. Intraspecific variation was found. Three‐dimensional surface heat maps revealed that shape complexity was driven by invaginations and protrusions of the vaginal wall. Phylogenetic signal was weak and metrics of natural selection (relative neonate size) and sexual selection (relative testes size, sexual size dimorphism, and penis morphology) did not explain vaginal complexity patterns. Additional metrics, such as penile shape complexity, may yield interesting insights into marine mammal genital coevolution. We advocate for the use of alpha shapes to discern patterns of evolution that would otherwise not be possible in 3D anatomical structures lacking homologous landmarks. [ABSTRACT FROM AUTHOR]

Few studies have explored the mating patterns of free‐ranging cetaceans, largely because of logistical challenges. We used an unmanned aerial vehicle (UAV) to follow and video‐record 25 groups of mating dusky dolphins (Lagenorhynchus obscurus) near the surface of the water and examine how behavior patterns varied with mating group type. We collected aerial footage of dolphins mating in traditional Isolated Pods and within Integrated Pods and compared differences in the number of mating animals, swimming speed, bearing change, percent time at the surface of the water, female respiration rate, copulatory position rate, and sex‐specific mating behaviors. Only the mean number of mating animals and some sex‐specific mating behaviors varied significantly between the two mating group types. More dolphins were engaged in mating behaviors in Isolated Pods than Integrated Pods. Males engaged in more interference behaviors in Isolated Pods compared to Integrated Pods. Females performed fewer speed bursts but more rolls on their backs in Integrated Pods compared to Isolated Pods. Several similarities and differences were found in comparison to boat‐based research of the same population of dolphins. We highlight the value of UAVs for noninvasive and accurate collection of cetacean behavioral data. [ABSTRACT FROM AUTHOR]

We evaluated whether morphological traits in capelin, Mallotus villosus, that appear to be sexually selected (pectoral fin, pelvic fin, anal fin, lateral ridge) were larger and more variable in males than females compared with naturally selected morphological traits (eyes, dorsal fin). Photographs were obtained of 136 capelin captured at two spawning sites and standardised measurements were taken of six morphological traits. Males had larger traits than females for a given body size and this was most pronounced in the traits thought to be sexually selected. Body size explained much of the variation in female traits but less variation in male traits, suggesting alternative selection pressures are involved. We suggest that larger male body size aids in endurance rivalry and sexually dimorphic traits help males to remain in physical contact with females while spawning on the beach. [ABSTRACT FROM AUTHOR]

In fission-fusion social systems with scramble competition between males, multiple males join mating groups while surrounding an oestrous female. If male decisions to join a mating group have been shaped by natural selection, then there should be an optimal group size resulting from the trade-offs between the benefits of monopolizing a female in small groups and the energy lost in defending her from rivals in large groups. Male dusky dolphins ( Lagenorhynchus obscurus) off Kaikoura, New Zealand, provide a unique opportunity to assess the optimum mating group size because they join transient mating groups not confounded by foraging or predator evasion. Within aggregations of up to 1000 individuals, males search for oestrous females, encountering choices of staying with a large mating group or leaving to find a smaller group. Mating groups typically involve multiple males mating with a single female. We conducted focal follows of mating groups (N = 44) by vessel from November 2011 through January 2012. We used video and a GPS to record group size, behaviour and movement. For each group, we measured potential costs ( Swim Speed, Loss of Monopolization Potential) and benefits ( Copulation Rate and Duration, Energy Savings). Only Loss of Monopolization Potential was positively correlated with group size, while Energy Savings was negatively correlated. Using these two factors as utility functions, we constructed an optimality model and predicted the optimal mating group size to be seven individuals with a range of 4-11 individuals due to variance. The observed modal mating group size was five dolphins, with a range of 2-15. We compare variation in mating group currencies and sizes to past studies. We discuss potential limitations of applying optimality models to predict mating group size for socially complex and behaviourally plastic species such as dolphins. [ABSTRACT FROM AUTHOR]