On reappearance and complexity in musical calling

Music is especially valued in human societies, but music-like behavior in the form of song also occurs in a variety of other animal groups including primates. The calling of our primate ancestors may well have evolved into the music of modern humans via multiple selective scenarios. But efforts to uncover these influences have been hindered by the challenge of precisely defining musical behavior in a way that could be more generally applied across species. We propose an acoustic focused reconsideration of “musicality” that could help enable independent inquiry into potential ecological pressures on the evolutionary emergence of such behavior. Using published spectrographic images (n = 832 vocalizations) from the primate vocalization literature, we developed a quantitative formulation that could be used to help recognize signatures of human-like musicality in the acoustic displays of other species. We visually scored each spectrogram along six structural features from human music—tone, interval, transposition, repetition, rhythm, and syllabic variation—and reduced this multivariate assessment into a concise measure of musical patterning, as informed by principal components analysis. The resulting acoustic reappearance diversity index (ARDI) estimates the number of different reappearing syllables within a call type. ARDI is in concordance with traditional measures of bird song complexity yet more readily identifies shorter, more subtly melodic primate vocalizations. We demonstrate the potential utility of this index by using it to corroborate several origins scenarios. When comparing ARDI scores with ecological features, our data suggest that vocalizations with diversely reappearing elements have a pronounced association with both social and environmental factors. Musical calls were moderately associated with wooded habitats and arboreal foraging, providing partial support for the acoustic adaptation hypothesis. But musical calling was most strongly associated with social monogamy, suggestive of selection for constituents of small family-sized groups by neighboring conspecifics. In sum, ARDI helps construe musical behavior along a continuum, accommodates non-human musicality, and enables gradualistic co-evolutionary paths between primate taxa—ranging from the more inhibited locational calls of archaic primates to the more exhibitional displays of modern apes.

Social selectivity and social motivation in voles

Selective relationships are fundamental to humans and many other animals, but relationships between mates, family members, or peers may be mediated differently. We examined connections between social reward and social selectivity, aggression, and oxytocin receptor signaling pathways in rodents that naturally form enduring, selective relationships with mates and peers (monogamous prairie voles) or peers (group-living meadow voles). Female prairie and meadow voles worked harder to access familiar vs. unfamiliar individuals, regardless of sex, and huddled extensively with familiar subjects. Male prairie voles displayed strongly selective huddling preferences for familiar animals, but only worked harder to repeatedly access females vs. males, with no difference in effort by familiarity. This reveals a striking sex difference in pathways underlying social monogamy, and demonstrates a fundamental disconnect between motivation and social selectivity in males-a distinction not detected by the partner preference test. Meadow voles exhibited social preferences but low social motivation, consistent with tolerance rather than reward supporting social groups in this species. Natural variation in oxytocin receptor binding predicted individual variation in prosocial and aggressive behaviors. These results provide a basis for understanding species, sex, and individual differences in the mechanisms underlying the role of social reward in social preference.

Ecology and social behaviour of the Mongolian gerbil: a generalised review

The present review provides a compilation of the published data on the ecology and social behaviour of Mongolian gerbils. Behavioural observations in the wild show that the Mongolian gerbil is a diurnal social rodent living in extended family groups. Seasonal breeding is typical of Mongolian gerbils in their natural habitat. Social monogamy seems to be characteristic of the Mongolian gerbil reproductive strategy, which however does not exclude facultative polygyny and promiscuity. A typical feature of the space use system in this species is territoriality. Social relationships in family groups may be defined as a subordination hierarchy. The hierarchy order is primarily determined by the age of the animals and maintained chiefly by the subordinates’ behaviour patterns. The complex social organisation in the Mongolian gerbil is characterised by cooperation in different activities. Cooperation appears to enhance the survival of family groups of this species under the extreme climatic conditions of Central Asia.

Medial amygdala ERα expression influences monogamous behaviour of male prairie voles in the field

Formation of long-term pair-bonds is a complex process, involving multiple neural circuits and is context- and experience-dependent. While laboratory studies using prairie voles have identified the involvement of several neural mechanisms, efforts to translate these findings into predictable field outcomes have been inconsistent at best. Here we test the hypothesis that inhibition of oestrogen receptor alpha (ERα) in the medial amygdala of male prairie voles would significantly increase the expression of social monogamy in the field. Prairie vole populations of equal sex ratio were established in outdoor enclosures with males bred for high levels of ERα expression and low levels of prosocial behaviour associated with social monogamy. Medial amygdala ERα expression was knocked down in half the males per population. Knockdown males displayed a greater degree of social monogamy in five of the eight behavioural indices assessed. This study demonstrates the robust nature of ERα in playing a critical role in the expression of male social monogamy in a field setting.

Social selectivity and social motivation in voles

Selective relationships are fundamental to humans and many other animals, but relationships between mates, family members, or peers may be mediated differently. We examined connections between social reward and social selectivity, aggression, and oxytocin receptor signaling pathways in rodents that naturally form enduring, selective relationships with mates and peers (prairie voles) or peers (meadow voles). Female prairie and meadow voles worked harder to access familiar vs. unfamiliar individuals, regardless of sex, and huddled extensively with familiar subjects. Male prairie voles also displayed strongly selective huddling preferences for familiar animals, but worked hardest to repeatedly access females vs. males, with no difference in effort by familiarity. This demonstrates a fundamental disconnect between motivation and social selectivity in males, and reveals a striking sex difference in pathways underlying social monogamy. Meadow voles exhibited social preferences but low social motivation, consistent with tolerance rather than reward supporting social groups in this species. Natural variation in oxytocin receptor genotype was associated with oxytocin receptor density, and both genotype and receptor binding predicted individual variation in prosocial and aggressive behaviors. These results provide a basis for understanding species, sex, and individual differences in the mechanisms underlying the role of social reward in social preference.

Ecological and Genetic Monitoring of a Recently Established Osprey (Pandion haliaetus) Population in Wales

ABSTRACT The Osprey (Pandion haliaetus) experienced severe declines in Europe over the past centuries, including extirpations from large parts of its range. After Ospreys began naturally recolonizing Wales, United Kingdom (UK), in 2004, the Dyfi Osprey Project initiated an extensive ecological (ringing, satellite tracking, and nest video recordings) and genetic (microsatellite genotyping) monitoring program alongside artificial nest platform construction. From 2004 to 2019 there were 40 reproductive events (i.e., eggs laid in a nest) across six nests, resulting in a total of 95 fledglings and a yearly average of 2.35 ± 0.8 (SD) fledglings per nest-with-eggs. Video recording at one nest documented high hatching success and survival to the fledging and dispersal phases, as well as mate- and nest-fidelity across multiple years. Collectively these breeding parameters suggest high productivity associated with artificial nest structures and limited density-dependent effects for the Welsh population due to its small size and low density at this stage of recovery. Satellite tracking of four migrating individuals revealed that Ospreys used a western European migratory flyway and wintered in sub-Saharan western Africa. Genetic analysis of nestlings from five nests indicated single paternity in all cases, in agreement with evidence of social monogamy. Genetic analysis of geographical outgroups (Scottish, Swedish, and Latvian) provided preliminary evidence of cryptic population structure among UK (Welsh and Scottish) populations. The novel combination of loci show Welsh Osprey retain high levels of variation and more broadly direct reconsideration of the hitherto inferred genetic poverty of the species compared to other raptors. We recommend implementation of similar long-term ecological and genetic monitoring programs for other populations.

Mate choice for major histocompatibility complex (MHC) complementarity in the Yellow-rumped Flycatcher (Ficedula zanthopygia)

Background Genes of the major histocompatibility complex (MHC) are an important component of the vertebrate immune system and play a significant role in mate choice in animal populations. However, the MHC genetic targets of female mate choice have not been clearly identified, and whether female mate choice is based on neutral genetic characteristics remains an open question. Here, we focus on the effects of morphological traits and genetic similarity among individuals in MHC class IIB (MHC IIB) exon 2 on mating in a sexually dimorphic songbird that exhibits social monogamy with extra-pair paternity (EPP). Methods We sequenced 64 parent–offspring triads sampled over a 3-year period using two MHC class II loci to detect disassortative mating in the Yellow-rumped Flycatcher (Ficedula zanthopygia). Results We found that MHC similarity in social pairs was lower than that in random pairs. Extra-pair mate choice according to MHC IIB was observed, in which females’ extra-pair mates had fewer MHC alleles than their within-pair mates, but there was no significant band-sharing between extra-pair sires and potential extra-pair mates. However, the interaction between the MHC diversity of females and that of the social males affected the occurrence of EPP. Conclusions Our results support the “optimality hypothesis” of MHC-based social and extra-pair choice. Female choice probably maintains a certain level of MHC diversity in offspring in the Yellow-rumped Flycatcher.

Absence of strict monogamy in the Eurasian jackdaw, Coloeus monedula

The Eurasian Jackdaw is thought to be archetypically monogamous, but recent tagging research uncovered extra-pair copulations in the species. Here we examined extra-pair paternity (genetic monogamy) in Eurasian jackdaws breeding in the Judean Hills, Israel, at the global edge of the species range, using a set of highly polymorphic molecular microsatellites. We found roughly a sixth of nests sampled showed deviations from monogamy, more than previously found in DNA fingerprinting studies of jackdaws, suggesting a mixed mating strategy in this population. These findings support the trend of extra-pair paternity in avian species, even when social monogamy remains the rule, and highlight the importance of continued study of species throughout their geographical range.

Reproduction

In this chapter the diverse mating systems exhibited by birds are described and explained. The chapter begins with a discussion of anisogamy and resulting behavioural differences exhibited by male and female birds. Sperm competition, sperm storage, and delayed fertilization are discussed and their consequences in terms of reproductive behaviours and systems are explained. Courtship systems and behaviours are discussed. Social monogamy, polygamy, and lekking behaviour are examined and examples of field research are given to support offered hypotheses. Bird song is considered in some detail through discussion of the function of song and of the genetic, neurological, and physiological control of singing. Particular attention is given to the impact of noise pollution on singing behaviour. The chapter concludes with a discussion of chick rearing including brood size management.