bluuebunny/crossref_metadata_2025_split huggingface dataset:
Infanticide and Sexual Conflict in Cetaceans
Authors: McEntee Molly H. F. , MacQueeney Meredith , Alvarado Diana , Mann Janet 
Published: September 2023

AbstractInfanticide by adult males is a striking example of sexual conflict; males can increase their reproductive success by killing an unrelated infant and accelerating the mother’s return to breeding condition. Reports of infanticide in cetaceans have quadrupled in the past decade, and infanticide has now been documented in six species of toothed whale, including multiple populations of common bottlenose dolphins (Tursiops truncatus). Evidence of infanticide in these species is consistent with the sexual selection hypothesis; perpetrators are predominantly adult males and targets are neonates. Toothed whales have long lactation periods that suppress estrus, making infanticide potentially adaptive for adult males. However, it remains unclear if infanticidal males are likely to sire the mother’s subsequent offspring. Here, we provide an overview of infanticide in cetaceans, evaluate the evidence for the sexual selection hypothesis, and propose a framework to predict infanticide risk in this clade. Toothed whales do not typically have dominance hierarchies, stable social groups, or monopolizable mating opportunities, all hallmarks of infanticide risk in terrestrial species. Instead, we hypothesize that infanticide risk in toothed whales is modulated by encounter rates with unfamiliar males.
Inter- and Intrapopulation Variation in Bottlenose Dolphin Mating Strategies
Authors: Brightwell Kristin , Gibson Quincy 
Published: September 2023

AbstractBottlenose dolphins (Tursiopsspp.) live in complex societies with high fission-fusion dynamics and exhibit a polygynandrous mating system in which both sexes mate with multiple partners. The benefits of polygynandry vary between the sexes; males likely increase their reproductive success by maximizing the number of mating partners, whereas females may reduce infanticide risk and/or increase the genetic quality of offspring by mating with multiple males. Socio-ecological theory states that mating strategies are dictated by the distribution of females and the ability of males to monopolize them. However, the tactics that males use to achieve reproductive success vary within and across populations. Although some male bottlenose dolphins appear to use a solitary approach to gain mating access, males in several populations demonstrate a relatively rare mating tactic: cooperative mate guarding within alliances. Male alliances generally consist of a pair or trio of males that work together to sequester a fertile female. However, nested or multilevel alliances have been documented in two populations to date (i.e., Shark Bay, Australia, and Jacksonville, Florida). The complexity of male alliances may vary in response to a suite of specific ecological, demographic, and/or morphological variables that promote male-male cooperation and reduce intrasexual competition. In this chapter, we review population-specific examples of male bottlenose dolphin mating tactics and examine several hypotheses that may explain inter- and intrapopulation variation in alliance complexity. We also explore the sociosexual behavior and potential countertactics used by females.
Sex and Sexual Strategies in Deep-Diving Risso’s Dolphins
Authors: Hartman Karin L. , van der Harst Pieter A. , Vilela Raul 
Published: September 2023

AbstractRisso’s dolphins (Grampus griseus) in the Azores maintain a sexually stratified community with males forming stable clusters, whereas females tend to associate in temporally stable units when calving and nursing. Large relative testes size indicates a mating system based on sperm competition. Small sexual size dimorphism and long interbirth intervals may facilitate male cooperation. We describe mating tactics observed in a resident population of Risso’s dolphins based on data collected over 8 consecutive years. We distinguished groups by sex and age class and analyzed peaceful and aggressive behaviors using an ethogram. Males displayed a variety of mating tactics described in cetaceans, spanning display, contest, endurance, and scramble competition, in the assumed context of sperm competition. We observed rare behaviors including male care for neonates but also intense aggression toward newborn calves, leading to possible infanticide. Females’ mating tactics included evasive behaviors and signal discrimination. We hypothesize that male mating tactics of Risso’s dolphins are related to age class. For females, the polygynandrous mating system may serve to improve fertility, reduce sexual harassment, and reduce the risk of infanticide. Adult females seem to prefer older over younger male groups, suggesting that some level of female mate choice exists in this species.
Sociosexual Behavior of Nocturnally Foraging Dusky and Spinner Dolphins
Authors: Markowitz Tim M. , Markowitz Wendy J. , Würsig Bernd , Orbach Dara N. 
Published: September 2023

AbstractDusky and spinner dolphins are small-bodied odontocetes that show variation in socioecology across their range. New Zealand dusky dolphins and Hawaiian spinner dolphins of deep nearshore waters feed nocturnally upon prey species associated with the deep scattering layer, leaving the daytime free for rest and social interaction, often close to shore. In this chapter, we investigate relationships between foraging ecology, diel activity patterns, and sociosexual activities of dusky and spinner dolphins in breeding and nonbreeding contexts. We review similarities and differences between dusky and spinner dolphins related to mating strategies and tactics, socioecology, and evolution. We examine the effects of breeding season and variation in male testis mass and female receptivity on mating behavior. We further explore the influence of sociosexual behavior on female social grouping and calf rearing.
Life History Parameters, Sociobiology, and Reproductive Strategies of Pilot Whales
Authors: Betty Emma L. , Zwamborn Elizabeth M. J. , Weyn Mieke , Luck Emma , Alves Filipe 
Published: September 2023

AbstractTwo species of pilot whales are globally distributed, the long-finned (Globicephala melas) in cold-temperate waters and the short-finned (G. macrorhynchus) in tropical and warm-temperate latitudes. Two subspecies of the long-finned pilot whale are recognized, G. m. melas in the North Atlantic and G. m. edwardii in the Southern Hemisphere. In addition, three types have been proposed in short-finned pilot whales. In general, it is assumed that pilot whales live in matrilineal societies composed of stable units/pods displaying bisexual natal philopatry, but inter- and intraspecific variabilities in the sociality of these units have been described worldwide. Moreover, there is inter- and intraspecific heterogeneity in life history and reproductive parameters, which supports geographic variation. To investigate life history parameters, sociobiology, and reproductive strategies within different populations of pilot whales, we reviewed the current literature and compiled novel data. We cover populations from both hemispheres and combine life history characteristics from strandings with field-/behavioral-based information such as long-term photographic-identification, social analysis with molecular sexing, and drone technology. This chapter contributes to improving our knowledge of the life history parameters between sexes and populations, interactions between animals of different sexes within units, social structures, and reproductive strategies in pilot whales. We explore pilot whales’ sexual group dynamics and social system and discuss whether they are strictly matrilineal in comparison with other “matrilineal” species.
Sex in Killer Whales: Behavior, Exogamy, and the Evolution of Sexual Strategies in the Ocean’s Apex Predator
Authors: Wright Brianna M. , Stredulinsky Eva H. , Ford John K. B. 
Published: September 2023

AbstractWe present the current available knowledge about sexual behavior and mating systems in the killer whale,Orcinus orca, focusing primarily on the most well-studied ecotype, the Residents of the eastern North Pacific. Resident killer whales display lifetime natal philopatry of both sexes and thus form stable social groupings organized along maternal lines. Inbreeding is minimized via exogamous mating during multigroup aggregations that are diffusely seasonal. Male reproductive success in Residents is highly skewed, likely as a result of female mate choice or possibly intrasexual contest competition (or both), with only the largest and oldest males siring offspring. Female choice for males with large body and appendage sizes likely explains why killer whales as a species have evolved a high degree of sexual dimorphism. Scarring patterns and dorsal fin injuries indicate that breeding-aged males may occasionally engage in aggressive intrasexual competition to secure mates. Young male Residents appear to practice courtship behaviors by engaging in sociosexual play with other males. Coercive mating or mate-guarding in this species has not been observed and appears to be unlikely. Relative testes size, penis length, and penis tip morphology indicate that some sperm competition presumably exists in killer whales and likely co-evolved with female polyandry. Thus, both pre- and postcopulatory sexual selection may occur simultaneously in killer whales, and this species probably has a polygynandrous mating system in which both males and females can breed with multiple partners. Genetic pedigree studies of killer whale ecotypes besides Residents are needed to provide currently lacking but valuable information about mating patterns in other populations.
Beaked Whale Sexual Dimorphism, Mating Strategies, and Diversification
Authors: Alves Filipe , Mesnick Sarah L. , Rosso Massimiliano , Pitman Robert L. 
Published: September 2023

AbstractBeaked whales (Ziphiidae), with 24 currently recognized species, are arguably the least known large animals on the planet, despite being widespread and at times abundant.Mesoplodon, with 16 currently recognized species, is by far the most speciose cetacean genus. Recent technological and taxonomic advances, long-term photographic-identification studies, and historical whaling data have allowed new insights into their social and mating strategies and how these may have driven diversification within the family. In most beaked whales, only adult males have exposed teeth—a single “tusk” erupts from each lower jaw and is used in contests to determine access to breeding females. How forcefully males of different species engage conspecifics varies widely based mainly on differences in tooth size/placement and jaw structure. We compiled data on key dimorphic traits including beak modification, tooth size and location, and prevalence of scarring in adults, for all beaked whales. More detailed information is given for the four best-studied species—northern bottlenose whale and Baird’s, Cuvier’s, and Blainville’s beaked whales. We then compared these traits with what is known about their social organization and reproductive anatomy to make inferences about mating strategies. More aggressive species tend to occur in small groups with only one dominant adult male present and have small testes relative to body size, suggesting that male reproductive success is largely determined by precopulatory contest competition and female defense polygyny. Less aggressive species tend to occur (at least at times) in larger, mixed-sex groups with multiple adult males present, and females may mate with multiple males, which favors postcopulatory sperm competition and polygynandry. We further discuss how conflicting pressures arising from males using their beaks for both feeding and fighting could have sparked an adaptive radiation in tooth development and beak morphology among beaked whales, especially withinMesoplodon, which would have had implications for male-male competition, social structure, sexual strategies, and, perhaps ultimately, evolutionary divergence and speciation within this group.
Sexual Behavior and Anatomy in Porpoises
Authors: Webber Marc A. , Keener William , Wahlberg Magnus , Elliser Cindy R. , MacIver Katrina , Ortiz Sara Torres , Jakobsen Freja , Hamel Héloïse , Rieger Alexandra , Siebert Ursula , Dunn Holly , Anderson David , Hall Anna M. , Birdsall Caitlin , Pielmeier Kate , Paiu Romulus-Marian , Boege Tobin Deborah D. , Orbach Dara N. 
Published: September 2023

AbstractAmong the taxonomic family of porpoises (Phocoenidae), mating behavior in nature has been described in detail only for the harbor porpoise (Phocoena phocoena). We review this species’ unusual mating habits based on a study in San Francisco Bay, California, USA, and present new data from across its range in the North Pacific, North Atlantic, Black Sea, and managed care. Results confirm the male’s unique laterality oriented solely to the female’s left side as contact occurred both in nature and managed care. The male’s high-energy sexual approach to the female led to splashy aerial behavior at the surface in nature. Drone footage provided observations of subsurface mating behavior, including evidence of male–male sexual interactions and a male calf interacting sexually with its mother. Harbor porpoise reproductive anatomy is also presented, with new comparative information on the vaquita (Phocoena sinus). The harbor porpoise’s lateralized behavior and anatomy (i.e., long asymmetric penis, large testes size, convoluted asymmetric female reproductive tract) may have coevolved. We note gaps in knowledge, suitable platforms for future investigations (drones, bridges, boats, and coastal cliffs), and what is known about mating behavior in other porpoise species, including hybridization. We conclude with conservation implications for porpoises and encourage researchers to recognize and report mating behavior as baseline data valuable for establishing marine conservation areas.
Genetic Tools to Investigate the Consequences of Sex
Authors: Gerber Livia , Krützen Michael 
Published: September 2023

AbstractThe primary purpose of sex is reproduction. However, because not all mating events result in fertilization and only a small number of species provide biparental care to their young, successfully reproducing individuals can rarely be identified from behavioral observations alone. Genetic tools permit reliable identification of an individual’s parents and thus of successfully reproducing individuals, because each parent passes on half of their genetic material to their offspring. In cetaceans, genetic tools are required to identify a female’s already weaned offspring and to detect successfully reproducing males due to the absence of paternal care. To date, relatively few studies have investigated variables linked to reproductive success in this taxon, owed to the difficulty of sampling entire cetacean populations. We summarize currently known factors that are linked to successful reproduction in whales, porpoises, and dolphins, as well as in terrestrial mammals with comparable life histories that give birth to single young.
Reproductive Tactics in Baleen Whales
Authors: Eichenberger Franca , Garland Ellen C. , Carroll Emma L. 
Published: September 2023

AbstractWhile a variety of reproductive tactics are readily witnessed in odontocetes, such behaviors can be far more elusive in baleen whales and in some cases are yet to be observed. This leads researchers to study the reproductive behaviors in mysticetes using a variety of research methods which have improved greatly in recent years. Genetics and genomics tools can provide valuable information on maternity, paternity, age, diversity, and kinship, while acoustic tools can provide new insights into the function of sexual displays such as song. In this chapter, we explore what is known about reproductive strategies and tactics of baleen whales, with a particular focus on the comparatively well-studied right whales (Eubalaena spp.) and humpback whale (Megaptera novaeangliae). Finally, we showcase that by integrating multiple data types, we can explore the interactions between anatomy, physiology, reproductive success, age, population dynamics, and acoustic displays to better understand the mating systems of baleen whales.
Bowhead Whale Reproductive Strategies
Authors: Koski William R. , George J. Craig , Würsig Bernd 
Published: September 2023

AbstractBowhead whales (Balaena mysticetus) have adopted growth and reproductive strategies to survive in a challenging environment where no other mysticete whales reside. They grow slowly, become sexually mature at around 25 years (later than other mammals), and do not give birth until they have sufficient energy reserves for the best possible chance of survival of the calf to weaning and long-term survival of the mother. To compensate for late maturity and long inter-birth intervals, some seem to have the capability to live to 200+ years of age, making them the longest-lived mammal known to date. Bowhead whale males have large testes per body size, and it is hypothesized that the basic polygynandrous system of females and males mating with multiple partners per estrous cycle allows for males to not compete violently against each other. Instead, they use sperm competition by volume of sperm for enhanced capability to father as many offspring as possible. Also, as in right whales (Eubalaena spp.), the length of the penis is proportionally longer than those of balaenopterids. Details of sperm volume, potential variabilities of sperm viabilities, and actual paternities are unknown, but some patterns can be inferred from the closely related right whales with similar morphologies.
Skulls, Teeth, and Sex
Authors: Loch Carolina , Fordyce R. Ewan , Werth Alexander 
Published: September 2023

AbstractMales and females of a species may differ in external appearance or other features. Sexual dimorphism often relates to mating behavior, via male-male competition for access to females (through direct fighting and/or indirect display), female choice of mates, or sexual conflict. In many mammals, skulls and teeth often display sexual dimorphism. Cetaceans show extraordinary variation in their dentition, and because teeth are often preserved, the evolutionary origins of these morphological novelties can be tracked in the fossil record. Sexual dimorphism has been proposed in several fossil cetaceans (i.e., pakicetids, protocetids, fossil beaked whales) and some odontocetes (notably Odobenocetops), and mainly inferred from differences in tooth size, skull dimensions, and thickening of skull bones. Within modern taxa, unusual differences in the dentition between the sexes have been observed in deep-diving beaked whales and arctic narwhals, the unicorns of the sea. Mandibular tusks in beaked whales are unusual because they erupt only in males, erupt only at sexual maturity, and protrude outside the mouth rather than projecting into the oral cavity. In beaked whales, the tusk-like dentition seems to have a minimal role in feeding, and functions as weapons or displays for intrasexual (e.g., male-male combat) and intersexual (e.g., female mate choice) competition, and possibly for female harassment by males seeking to mate. In narwhals, the long and spiralled left tusk commonly only erupts in males and is presumed to play a prominent role in male-male fighting or displays for female mate choice. Except for narwhals and beaked whales, sexual dimorphism in skull and dental structures is not prominent in cetaceans. However, we still do not know whether functional aspects such as enamel structure and thickness, mechanical properties, and chemical composition of dental tissues may vary between males and females.
Cetacean Evolution: Copulatory and Birthing Consequences of Pelvic and Hindlimb Reduction
Authors: Cooper Lisa Noelle , Suydam Robert , Thewissen J. G. M. 
Published: September 2023

AbstractThe earliest fossil cetaceans (archaeocetes) dramatically shifted the shape and articulation of the pelvis and hindlimbs during the land-to-sea transition. Archaeocetes were mostly semi-aquatic “walking whales” that used powerful hindlimbs to walk on land and swim to reach new aquatic sources of food. However, skeletons of the latest diverging lineages of archaeocetes, the basilosaurids, showed that the pelvis initially lost articulation with the sacrum, and hindlimbs were reduced and encased within the body wall. Consequently, basilosaurids were no longer able to bear their weight on land and probably had a different mating strategy compared to the other archaeocetes. Basilosaurid mating behaviors were probably consistent with those of modern cetaceans, including lateral- and ventral-facing copulation. Moreover, a pelvic girdle that was no longer constrained by vertebral and limb attachments likely freed fetal development from size constraints at birth, allowing for the birth of large fetuses. This study reports new data showing growth of the pelvis with age in modern bowhead whales (Balaena mysticetus) and their implications for left-right asymmetry and sex difference in pelvic dimensions among modern cetaceans. Reproductive structures present in modern cetaceans and artiodactyls were probably present in archaeocetes, including pelvic attachment of muscles associated with erection and mobility of the penis, the ischiocavernosus, in males and the clitoris of females. Within females, transverse folds along the vaginal canal are present in some terrestrial artiodactyls, modern cetaceans, and probably archaeocetes. Vaginal folds were probably exapted to assist in successful aquatic copulation in all fossil and modern cetaceans as they may protect some sperm from the lethal effects of sea water. Taken together, shifts in the pelvic girdle of cetaceans occurred over 40 million years ago and probably required changes in mating behaviors that were consistent with those seen in modern cetaceans.
Sexual Anatomy of Female Cetaceans: Art and Science Contribute Insights into Functionality
Authors: Orbach Dara N. , Gorter Uko , Mesnick Sarah 
Published: September 2023

AbstractThe relationship between sexual selection and the diversity and rapid evolution of male genitalia has been well-documented across many animal taxa, while the morphological variability of female genitalia has received comparatively little attention. Female whales, dolphins, and porpoises possess unusual flaps, folds, and blind sacs in their vaginas, which vary among taxa and may serve several functions. We review the relationship between form and function of these unusual vaginal structures in cetaceans and discuss evidence that supports or refutes various functional hypotheses. A compilation of three-dimensional vaginal endocast models, contemporary high-resolution photographs of dissected reproductive tracts, and detailed anatomical illustrations ranging over 175 years are used to highlight the diversity of forms and fill in gaps in taxonomic knowledge. We discuss the complementary nature of anatomical illustrations and modern analytical and visual tools and how they can help us better understand the evolution of such unusual morphological structures. We identify opportunities for future studies in cetacean genital evolution and discuss the insights they may provide into mating strategies of cetaceans.