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Vocal activity and signal characteristics of mammals are driven by several factors that result in both stability and plasticity over multiple time scales. All three extant species of manatee communicate with several calls that are especially important for maintaining contact between cows and calves. Determining if calf calls differ across manatee species will provide insights into the evolution of species-specific acoustic communication traits. We investigated the interspecific differences in the vocalizations of calves of Amazonian manatees (Trichechus inunguis) and the two subspecies of the West Indian manatee (T. manatus). Vocalizations of individual calves were recorded in rehabilitation centers in Brazil, Puerto Rico, the United States, and Mexico. The acoustic structure of calls produced by manatee calves varied between species and with body size. Amazonian manatee calves produced shorter calls with multiple notes at higher frequency while West Indian calves produced modulated calls that were lower in frequency and longer in duration. Smaller West Indian calves produced frequency modulated, hill-shaped calls that flattened with an increase in body length. Our results provide evidence for divergence in the ontogeny of vocalizations across T. manatus and T. inunguis and suggest variation in body size contributed to the evolution of differences in the characteristics of their calls., (© 2022. The Author(s).)

Mating with multiple partners is common across species, and understanding how individual males secure fertilization in the face of competition remains a fundamental goal of evolutionary biology. Game theory stipulates that males have a fixed budget for reproduction that can lead to a trade-off between investment in precopulatory traits such as body size, armaments, and ornaments, and postcopulatory traits such as testis size and spermatogenic efficiency. Recent theoretical and empirical studies have shown that if males can monopolize access to multiple females, they will invest disproportionately in precopulatory traits and less in postcopulatory traits. Using phylogenetically controlled comparative methods, we demonstrate that across 58 cetacean species with the most prominent sexual dimorphism in size, shape, teeth, tusks, and singing invest significantly less in relative testes mass. In support of theoretical predictions, these species tend to show evidence of male contests, suggesting there is opportunity for winners to monopolize access to multiple females. Our approach provides a robust dataset with which to make predictions about male mating strategies for the many cetacean species for which adequate behavioral observations do not exist., (© 2015 The Author(s). Evolution © 2015 The Society for the Study of Evolution.)

Twenty nine cetacean species occur in Costa Rican waters but extensive research has been conducted only for three species. The latter shows there is a lack of general and local information about these mammals, even when the country, has shown a remarkable growth in whale watching activities. The increasing use of marine resources in coastal areas has also developed the need to determine the occurrence of cetaceans in areas showing high tourist presence, in order to propose sound conservation measures. In this study, environmental variables were determined and subsequently related to the presence of the species recorded, out of 166 sightings, between 2005 and 2006. The species with highest proportion of sightings were Stenella attenuata (68%), followed by Megaptera novaeangliae (13%) and Tursiops truncatus (10%). The presence of spotted dolphins is related to changes in salinity and water transparency, while that of the humpback whale was related to wave height (Beaufort scale) and water temperature. The presence of seven species of cetaceans was confirmed in two coastal areas of the Pacific coast of Costa Rica, from which three are present throughout the year. Environmental variables were found related to the presence of at least two species.

In the mid 1990s cytochrome b and other mitochondrial DNA data reinvigorated cetacean phylogenetics by proposing many novel and provocative hypotheses of cetacean relationships. These results sparked a revision and reanalysis of morphological datasets, and the collection of new nuclear DNA data from numerous loci. Some of the most controversial mitochondrial hypotheses have now become benchmark clades, corroborated with nuclear DNA and morphological data; others have been resolved in favor of more traditional views. That major conflicts in cetacean phylogeny are disappearing is encouraging. However, most recent papers aim specifically to resolve higher-level conflicts by adding characters, at the cost of densely sampling taxa to resolve lower-level relationships. No molecular study to date has included more than 33 cetaceans. More detailed molecular phylogenies will provide better tools for evolutionary studies. Until more genes are available for a high number of taxa, can we rely on readily available single gene mitochondrial data? Here, we estimate the phylogeny of 66 cetacean taxa and 24 outgroups based on Cytb sequences. We judge the reliability of our phylogeny based on the recovery of several deep-level benchmark clades. A Bayesian phylogenetic analysis recovered all benchmark clades and for the first time supported Odontoceti monophyly based exclusively on analysis of a single mitochondrial gene. The results recover the monophyly of all but one family level taxa within Cetacea, and most recently proposed super- and subfamilies. In contrast, parsimony never recovered all benchmark clades and was sensitive to a priori weighting decisions. These results provide the most detailed phylogeny of Cetacea to date and highlight the utility of both Bayesian methodology in general, and of Cytb in cetacean phylogenetics. They furthermore suggest that dense taxon sampling, like dense character sampling, can overcome problems in phylogenetic reconstruction.

Nineteen species of cetaceans (families Balaenopteridae, Kogiidae, Physeteridae, Ziphiidae and Delphinidae) occur in the Costa Rican Pacific Exclusive Economic Zone (EEZ). Based on data recorded from the EEZ by the Southwest Fisheries Service Center, Cascadia Research Collective, and CIMAR between 1979-2001, we mapped the distribution of 18 cetacean species. Our results suggest that the majority of the cetacean species use primarily oceanic waters, particularly those species within the families Balaenopteridae, Kogiidae. Physeteridae and Ziphiidae. Members of the family Delphinidae showed a wide variety of distribution patterns: seven species are widespread throughout the EEZ, four appear to be exclusively pelagic, and two are primarily coastal. Overall, three cetacean species appear to have populations concentrated in coastal waters: Stenella attenuata graffmani. Tursiops truncatus, and Megaptera novaeangliae. These three may be more susceptible to human activities due to the overlap of their ranges with fishery areas (tuna and artisanal fisheries), and an uncontrolled increase of touristic whale watching activities in several parts of their range. The distribution maps represent the first comprehensive representation of cetacean species that inhabit Costa Rican Pacific waters. They provide essential base-line information that may be used to initiate conservation and management efforts of the habitats where these animals reproduce and forage.

Dolphins are characterized by a significant behavioral versatility, which allows them to respond to environmental seasonality. Seasonal variation in dolphin behavior in tropical waters is not well known. Stenella attenuata graffmani is a resident dolphin in the clearly defined seasonal Gulf of Papagayo, Costa Rica, and we studied if dolphin group size, occurrence and behavioral patterns were associated with season and time of day in the gulf. Using strip transects we surveyed two locations for three consecutive years. School size ranged from 1 to 50 individuals, mean group size was 10.16 (SD = 9.61) individuals. Overall, foraging activities were the most frequent, followed by social interactions and travel. From 6:00 AM to 9:00 AM we mostly observed social interactions, followed by feeding-socializing (9:00 AM-12:00 PM) and feeding exclusively (12:00 PM-3:00 PM). Social activities intensified afterwards (3:00 PM-6:00 PM). Behavior and gulf seasonality were associated (chi2 = 90.52, gl = 6, p<0.05, n = 99). In the dry season (December-April) feeding predominated over other activities, but socializing was more frequent in the early rainy season (May-July). Larger groups (mean 12 dolphins) forage actively; smaller groups (mean 6 dolphins 6.51 +/- 5.12) foraged more passively. Seasonal variation in dolphin activities are likely to be associated with food availability, as observed in the high number of groups involved in foraging behaviors, and a high investment in foraging activities during the dry season.