When will the stork arrive? Patterns of birth seasonality in neotropical primates

Mammalian Life History: Weaning and Tooth Emergence in a Seasonal World

The young of toothed mammals must have teeth to reach feeding independence. How tooth eruption integrates with gestation, birth and weaning is examined in a life-history perspective for 71 species of placental mammals. Questions developed from high-quality primate data are then addressed in the total sample. Rather than correlation, comparisons focus on equivalence, sequence, the relation to absolutes (six months, one year), the distribution of error and adaptive extremes. These mammals differ widely at birth, from no teeth to all deciduous teeth emerging, but commonalities appear when infants transit to independent feeding. Weaning follows completion of the deciduous dentition, closest in time to emergence of the first permanent molars and well before second molars emerge. Another layer of meaning appears when developmental age is counted from conception because the total time to produce young feeding independently comes up against seasonal boundaries that are costly to cross for reproductive fitness. Mammals of a vast range of sizes and taxa, from squirrel monkey to moose, hold conception-to-first molars in just under one year. Integrating tooth emergence into life history gives insight into living mammals and builds a framework for interpreting the fossil record.

Odours of caterpillar-infested trees increase testosterone concentrations in male great tits

Trees release Herbivore-Induced Plant Volatiles (HIPVs) into the air in response to damage inflicted by insects. It is known that songbirds use those compounds to locate their prey, but more recently the idea emerged that songbirds could also use those odours as cues in their reproductive decisions, as early spring HIPVs may contain information about the seasonal timing and abundance of insects. We exposed pre-breeding great tits (Parus major) to the odours of caterpillar-infested trees under controlled conditions, and monitored reproduction (timing of egg laying, number of eggs, egg size) and two of its main hormonal drivers (testosterone and 17β-estradiol in males and females, respectively). We found that females exposed to HIPVs did not advance their laying dates, nor laid larger clutches, or larger eggs compared to control females. 17β-estradiol concentrations in females were also similar between experimental and control birds. However, males exposed to HIPVs had higher testosterone concentrations during the egg-laying period. Our study supports the hypothesis that insectivorous songbirds are able to detect minute amounts of plant odours. The sole manipulation of plant scents was not sufficient to lure females into a higher reproductive investment, but males increased their reproductive effort in response to a novel source of information for seasonal breeding birds.

Direct links between resource availability and activity budget better reveal ecological patterns of endangered Coimbra-Filho's titi monkey

Many primatological studies do not assess direct indexes of food availability to make inferences about behavioral strategies. We related the diet and behavior of a group of Callicebus coimbrai in northeastern Brazil to fruit availability indexes and compared this pattern between seasons (direct and indirect assessment of food availability) to assess whether direct and indirect approaches detect similar ecological patterns. We monitored the study group for 33 months (5 days/month) via scan sampling. The monthly availability of fruits and new leaves was recorded in phenological transects. Fruit availability varied across years based on fruit prevalence, and timing and duration of the abundant seasons. We did not find evidence of a time-minimizing strategy, since C. coimbrai did not change its activity levels according to food availability. However, the negative relationship between foraging and fruit availability indicates that C. coimbrai can compensate for the lower fruit availability by increasing the search for alternative food sources. Monthly fruit consumption was positively correlated to fruit availability and negatively related to the consumption of other food items. However, the behavioral and feeding profiles did not vary between seasons and were not related to rainfall levels. Primate studies should directly relate behavioral and feeding profiles to fruit availability indices, thus avoiding using seasons as proxies of food availability.

Homosexual Courtship in Young Wild Capuchin Monkeys: A Case Study

In primates, many species exhibit same-sex sexual behaviors (SSB), defined as "genital contact or genital manipulation between same-sex individuals." Several sociosexual functions have been proposed, including proceptivity enhancement, receptivity reduction, dominance assertion, practice for heterosexual copulation, tension regulation, reconciliation, and alliance formation. Capuchin monkeys are known for their rich and flexible sexual behavioral repertoire and elaborated courtships. At present, the few reports of SSB in capuchin monkeys (genera Sapajus and Cebus) focused on mounting. Here, we describe the case observed in a population of wild yellow-breasted capuchin monkeys (Sapajus xanthosternos) in which two young males, aged 5-6 years and 19 months, performed a 15-min uninterrupted sequence of courtship behaviors and mounting. Comparing with a previously established ethogram of 20 behaviors typical for heterosexual behavior of tufted capuchins, we show that these males performed 16 of them. Thus, SSBs are already present in the repertoire of young individuals and the practice may serve to create or strengthen bonds. Although same-sex mounting and genital inspection are common in capuchins' play and other social interactions, the almost entire array of courtship behaviors has never been observed in youngsters. Additionally, this example supports the notion that primate (homo)sexual behavior is not limited to genitalia and copulation, since the observed courtship included diverse behaviors different from genital contact. Thus, we propose a broader definition of sexual behavior.

A 24-Year Record of Female Reproductive Dynamics in Two Sympatric Mouse Lemur Species in Northwestern Madagascar

Seasonal reproduction is widespread among primates but the degree of reproductive synchrony and plasticity can vary, even between closely related species. This study compares the dynamics of female reproductive seasonality in two mouse lemur species, Microcebus murinus and M. ravelobensis, in Ankarafantsika National Park, Madagascar, across 24 years. We collected 4321 records of female reproductive state from 1033 individual females (319 M. murinus, 714 M. ravelobensis). The analyses revealed disparate reproductive schedules: While female M. murinus showed high degrees of reproductive synchrony throughout all years, leading to the production of two successive litters, the seasonal onset of estrus (= reproductive activation) in female M. ravelobensis was more flexible than in M. murinus, starting 2-4 weeks earlier, varying by up to 4 weeks between years, and being less synchronized. M. ravelobensis females became reproductively active later in years with more rainfall, in particular rain in February, but the timing of reproductive activation was not related to differences in temperatures. The likelihood of early conception was significantly lower in M. ravelobensis than in M. murinus. This was partly due to delayed reproductive activation in young animals, and a lower likelihood of early conception for females with low body mass in M. ravelobensis. Our results suggest high, adaptive reproductive plasticity in M. ravelobensis that may enable individuals to respond flexibly to yearly environmental changes and expand the reproductive period under favorable conditions. These species differences in reproductive schedules may be the result of the divergent evolutionary histories of the two mouse lemur species in different parts of Madagascar.

Habitat characteristics and life history explain reproductive seasonality in lagomorphs

Lagomorphs show extensive seasonal variation in their reproduction. However, the factors causing this large variation have so far mostly been investigated intraspecifically and therefore provide only some exemplary comparisons of lagomorph reproductive seasonality. The present study applies both a categorical description (birth season categories 1–5) and a quantitative measure (birth season length in months) to summarize the degree of birth seasonality in the wild of 69 lagomorph species. Using a comparative approach, I tested the influence of 13 factors, comprising six habitat, five life history and two allometric variables on birth season length in lagomorphs. Leporids mainly show non-seasonal birthing patterns with high intraspecific variation. Their opportunistic breeding strategy with high reproductive output and their large distribution areas across wide latitude and elevation ranges might be the reasons for this finding. Ochotonids reproduce strictly seasonally, likely because they live at northern latitudes, are high-altitude specialists, and occur in limited distribution areas. The most important factors associated with variation in lagomorph birth seasonality are mid-latitude, mean annual temperature and precipitation of a species’ geographical range and life history adaptations including fewer but larger litters in seasonal habitats. Birth seasons become shorter with increasing latitude, colder temperatures, and less precipitation, corresponding to the decreasing length of optimal environmental conditions. Leporid species with shorter breeding seasons force maternal resources into few large litters to maximise reproductive output while circumstances are favourable. Since allometric variables were only weakly associated with reproductive seasonality, life history adaptations and habitat characteristics determine birth seasonality in Lagomorpha.

Dramatic decline in a titi monkey population after the 2016-2018 sylvatic yellow fever outbreak in Brazil

Platyrrhini are highly vulnerable to the yellow fever (YF) virus. From 2016 to 2018, the Atlantic Forest of southeast Brazil faced its worst sylvatic YF outbreak in about a century, thought to have killed thousands of primates. It is essential to assess the impact of this epidemic on threatened primate assemblages to design effective conservation strategies. In this study, we assessed the impact of the 2016-2018 YF outbreak on a geographically isolated population of Near Threatened black-fronted titi monkeys (Callicebus nigrifrons) in two Atlantic Forest patches of the Santuário do Caraça, MG, Brazil. Extensive preoutbreak monitoring, conducted between 2008 and 2016, revealed that the home range and group sizes of the population remained stable. In 2016, the population size was estimated at 53-57 individuals in 11-12 groups. We conducted monitoring and playback surveys in 2019 and found that the population had decreased by 68% in one forest patch and completely vanished in the other, resulting in a combined decline of 80%. We discuss this severe loss of a previously stable population and conclude that it was highly likely caused by the YF outbreak. The remaining population is at risk of disappearing completely because of its small size and geographic isolation. A systematic population surveys of C. nigrifrons, along other sensible Platyrrhini species, is needed to re-evaluate their current conservation status.

Theoretical constraints: Science, caretaking, and the creation of normative ideals

OBJECTIVES

This review explores the dualism in evolutionary anthropology that both acknowledges a broad range of familial caretaking strategies, while also remaining tethered to theories scaffolded around notions of selfish genes that constrain our understanding of who provides adequate kin care. I examine the process of norm creation in the sciences by investigating how theory may limit which data are collected and how those data are interpreted.

METHODS

This paper serves as a literature review and critique of prominent biological, evolutionary, and psychological conceptualizations of parental investment and caretaking in humans, and how these studies shape what is considered normal behavior in scientific literature.

RESULTS

Quantification, assessment, and theory building in evolutionary anthropology, and an oversampling of WEIRD communities in other disciplines, have limited our understanding of what constitutes both evolutionarily adaptive behaviors, and culturally specific human behaviors.

CONCLUSIONS

A synthetic theoretical model of behavioral norms in childrearing must account for an exchange of psycho-social and cultural resources and skills, the transfer of energetic reserves via gestation and lactation, and the indirect benefits of genetic inheritance. The emphasis on tailoring data collection to fit evolutionary theories of the family has limited our ability to understand the diverse proximate mechanisms that humans employ in taking care of kin as biocultural reproducers.

Associations between fecal cortisol and biparental care in a pair-living primate

OBJECTIVES

We quantified variation in fecal cortisol across reproductive periods in Azara's owl monkeys (Aotus azarae) to examine physiological mechanisms that may facilitate biparental care. Specifically, we evaluated evidence for the explanation that owl monkeys have hormonal mechanisms to mobilize energy during periods when each sex is investing heavily in reproduction, that is, the gestation period for females and the infant care period for males.

MATERIALS AND METHODS

Between 2011 and 2015, we monitored 10 groups of Azara's owl monkeys from a wild population in Formosa, Argentina and collected fecal samples from 26 adults (13 males, 13 females). Using enzyme-linked immunosorbent assays, we quantified fecal cortisol as a proxy for evaluating stress responses, including energetic demands, on both sexes during periods of reproduction and parental care.

RESULTS

Male cortisol was lowest during periods when they were caring for young infants (<3 months) compared with periods with older infants or no infant. Female cortisol was elevated during gestation compared with other periods. Mean fecal cortisol in both males and females was lower when an infant was present compared with when females were gestating.

DISCUSSION

Our results do not support the hypothesis that owl monkey males have elevated fecal cortisol during periods when they need to mobilize energy to provide intensive infant care. Our findings are also inconsistent with the Maternal Relief hypothesis. However, results from studies measuring fecal cortisol must be interpreted with care and alternative explanations, such as seasonal fluctuations in diet and thermoenergic demands, should be considered when drawing conclusions.

Reproductive seasonality in two sympatric primates (Ateles belzebuth and Lagothrix lagotricha poeppigii) from Amazonian Ecuador

With their large body size and "slow" life histories, atelin primates are thought to follow a risk-averse breeding strategy, similar to capital breeders, in which they accumulate energy reserves in anticipation of future reproductive events such as gestation and lactation. However, given the paucity of longitudinal data from wild populations, few studies to date have been able to compare the timing of reproductive events (e.g., copulations, conceptions, and births) in relation to shifting resource availability over multiple years. We examined the reproductive patterns of two atelin species-white-bellied spider monkeys (Ateles belzebuth) and lowland woolly monkeys (Lagothrix lagotricha poeppigii)-in relation to habitat-wide estimates of fruit availability at the Tiputini Biodiversity Station (TBS) in Amazonian Ecuador. Our sample included 4 years of data on births (N = 36) and copulations (N = 170) for Lagothrix, 10 years of data on births (N = 35) and copulations (N = 74) for Ateles, and 7 years of data on ripe fruit availability. Reproductive events were distinctly seasonal. For both species, births were concentrated between May and September, a time period in which ripe fruit was relatively scarce, while inferred conceptions occurred between September and January, when ripe fruit availability was increasing and maintained at high-levels throughout the forest. Interannual variation in births was relatively stable, except for in 2016 when twice as many infants were born following a strong El Niño event that may have led to unusually high levels of fruit productivity during the 2015 breeding season. Although copulations were observed year-round, an overwhelming majority (>90% for Lagothrix and >80% for Ateles) took place between August and February when females were most likely to conceive. Collectively, these data follow the reproductive patterns observed in other atelin primates, and, as proposed by others, suggest that atelins may follow a risk-averse breeding strategy.

Reproductive seasonality in primates: patterns, concepts and unsolved questions

Primates, like other mammals, exhibit an annual reproductive pattern that ranges from strictly seasonal breeding to giving birth in all months of the year, but factors mediating this variation are not fully understood. We applied both a categorical description and quantitative measures of the birth peak breadth based on daily observations in zoos to characterise reproductive seasonality in 141 primate species with an average of 941 birth events per species. Absolute day length at the beginning of the mating season in seasonally reproducing species was not correlated between populations from natural habitats and zoos. The mid-point of latitudinal range was a major factor associated with reproductive seasonality, indicating a correlation with photoperiod. Gestation length, annual mean temperature, natural diet and Malagasy origin were other important factors associated with reproductive seasonality. Birth seasons were shorter with increasing latitude of geographical origin, corresponding to the decreasing length of the favourable season. Species with longer gestation periods were less seasonal than species with shorter ones, possibly because shorter gestation periods more easily facilitate the synchronisation of reproductive activity with annual cycles. Habitat conditions with higher mean annual temperature were also linked to less-seasonal reproduction, independently of the latitude effect. Species with a high percentage of leaves in their natural diet were generally non-seasonal, potentially because the availability of mature leaves is comparatively independent of seasons. Malagasy primates were more seasonal in their births than species from other regions. This might be due to the low resting metabolism of Malagasy primates, the comparatively high degree of temporal predictability of Malagasy ecosystems, or historical constraints peculiar to Malagasy primates. Latitudinal range showed a weaker but also significant association with reproductive seasonality. Amongst species with seasonal reproduction in their natural habitats, smaller primate species were more likely than larger species to shift to non-seasonal breeding in captivity. The percentage of species that changed their breeding pattern in zoos was higher in primates (30%) than in previous studies on Carnivora and Ruminantia (13 and 10%, respectively), reflecting a higher concentration of primate species in the tropics. When comparing only species that showed seasonal reproduction in natural habitats at absolute latitudes ≤11.75°, primates did not differ significantly from these two other taxa in the proportion of species that changed to a less-seasonal pattern in zoos. However, in this latitude range, natural populations of primates and Carnivora had a significantly higher proportion of seasonally reproducing species than Ruminantia, suggesting that in spite of their generally more flexible diets, both primates and Carnivora are more exposed to resource fluctuation than ruminants.

Synchronization of weaning time with peak fruit availability in squirrel monkeys (Saimiri collinsi) living in Amazonian Brazil

Many mammals coincide their reproductive activities with factors such as ambient temperature, rainfall, and food availability. In primates that invest immediate food intake into reproduction, the periods of maximum fruit production often coincide with the peak of lactation (to maximize maternal survival) or the occurrence of weaning (to maximize infant survival). This study investigates the relationship between reproductive periods and the availability of ripe fruit in the habitat of a population of wild squirrel monkeys (Saimiri collinsi) in Amazonian Brazil. We combine data from several years (2002-2003; 2011-2015) during which we followed the monkeys and quantified the occurrence of matings, gestations, births, and the number of lactating females. We also collected rainfall and plant phenological data for 24 months. Our results confirm that reproductive events are highly seasonal in S. collinsi. The period of weaning corresponded to the peak in the abundance of ripe fruits consumed by the monkeys. This indicates that the period of infant nutritional independence is optimally timed to coincide with periods of greater food production in this habitat. We suggest that seasonal breeding in these primates does not necessarily reduce maternal energetic stress, but likely improves infant survivorship.

A longitudinal assessment of behavioral development in wild capuchins: Personality is not established in the first 3 years

Animal personality is defined as consistent individual differences across time and situations, but little is known about how or when those differences are established during development. Likewise, several studies described the personality structure of adult capuchin monkeys, without assessing the ontogeny of these personality traits. We analyzed the behavioral repertoire of 12 wild infants (9 males, 3 females) yellow-breasted capuchin monkeys (Sapajus xanthosternos), in Una Biological Reserve (Bahia, Brazil). Each infant was observed and filmed weekly from birth until 36 months, through daily focal sampling. We analyzed the behavior of each individual in 10 developmental points. By means of component reduction (principal component analysis), we obtained four behavioral traits: Sociability, Anxiety, Openness, and Activity. We investigated whether there were developmental effects on those traits by fitting regression models for the effect of time on behavioral traits, controlling for monkey identity, sex, and cohort. Sociability (decreasing) and Anxiety (increasing) changed significantly along development. By means of repeatability analysis, we did not find intra-individual consistency across time in those traits, so we cannot discriminate stable personality traits in early ontogeny. Our results show that the personality structure of capuchin monkeys is not established during early development, in agreement with the literature on human personality.

Differential responses of non-human primates to seasonal temperature fluctuations

Non-human primates (NHPs) can adapt to conditions outside of their natural habitat and climatic ranges but this can be influenced by inherent evolutionary traits or plasticity of species that evolved in diverse environmental conditions. In this study, we investigated how five species of NHPs that have natural distributions across a range of climatic conditions responded to seasonal temperature changes in a captive environment. The activity levels of NHPs were affected by temperature changes over the season, where activity levels were generally reduced at the lower and higher temperature ranges. Species that are naturally found within narrower and warmer climatic ranges, compared to those found in colder environments with wider fluctuations in temperature, showed more marked changes in activity levels in response to temperature changes. In lower temperature conditions, three out of five species showed significantly lower activity levels; whereas in higher temperature conditions, the activity levels of all species did not significantly decrease. The frequency of thermoregulation behaviours was higher, and use of artificial thermoregulatory sources lower, for species that did not substantially adjust their activity levels in different temperature conditions. Our results suggest that NHPs largely retained the evolutionary traits related to thermoregulation, according to the different ambient conditions they evolved in and may have low behavioural plasticity in adapting to conditions outside of their natural ranges. These results provide insights for improving conservation and captive management and may have implications for understanding NHP resilience to the increasing impact of global climate change.

Testing the weekend effect hypothesis: Time of day and lunar phase better predict the timing of births in laboratory-housed primates than day of week

The weekend effect hypothesis proposes that captive primates are more likely to give birth during times of low disturbance and reduced staff activity. The hypothesis specifically predicts that laboratory-housed primates will be more likely to give birth during the weekend than weekdays when staff activity is reduced. To date, support for the weekend effect hypothesis has been mixed and based on studies with relatively few subjects. To further examine the hypothesis, we analyzed the birthing patterns of three genera of laboratory-housed primates: squirrel monkeys (Saimiri species, N = 2,090 births), owl monkeys (Aotus species, N = 479 births), and rhesus macaques (Macaca mulatta, N = 2,047 births). Contrary to predictions derived from the weekend effect hypothesis, the frequencies of births during weekends for all taxa were not significantly different from rates that would be expected by chance. However, while there was no variance across days of the week, all three taxa gave birth at nighttime, when staff was absent. This parallels reports of births in wild and captive monkeys, both diurnal and nocturnal, which are more likely to give birth during the night; plausibly a time when the environmental and social disturbance is lowest and the mother is safest to bond with her newborn infant. As all births occurred at night, we also explored the relationship between the lunar cycle and the timing of births timing. While the diurnal primates (i.e., Saimiri and Macaca) were no more likely to give birth on "bright" nights than "dark" nights, owl monkeys (Aotus) had a much higher frequency of births on bright nights than darker ones, and at rates that deviated from chance. Our data provide a more detailed understanding on how the environment may influence captive monkey births but do not support the oft-cited weekend effect hypothesis.

Social and ecological drivers of reproductive seasonality in geladas

Many nonseasonally breeding mammals demonstrate some degree of synchrony in births, which is generally associated with ecological factors that mediate fecundity. However, disruptive social events, such as alpha male replacements, also have the potential to affect the timing of female reproduction. Here, we examined reproductive seasonality in a wild population of geladas (Theropithecus gelada) living at high altitudes in an afro-alpine ecosystem in Ethiopia. Using 9 years of demographic data (2006-2014), we determined that, while females gave birth year-round, a seasonal peak in births coincided with peak green grass availability (their staple food source). This post-rainy season "ecological peak" in births meant that estimated conceptions for these births occurred when temperatures were at their highest and mean female fecal glucocorticoid concentrations were at their lowest. In addition to this ecological birth peak, we also found a separate birth peak that occurred only for females in groups that had experienced a recent replacement of the dominant male (i.e., a takeover). Because new dominant males cause abortions in pregnant females and kill the infants of lactating females, takeovers effectively "reset" the reproductive cycles of females in the group. This "social birth peak" was distinct from the ecological peak and was associated with higher rates of cycling and conceptions overall and higher glucocorticoid levels immediately following a takeover as compared to females that did not experience a takeover. These data demonstrate that social factors (in this case, male takeovers) can contribute to population-level reproductive seasonality above and beyond group-level reproductive synchrony.

Ontogenetic and functional modularity in the rodent mandible

The material properties of diets consumed by juvenile individuals are known to affect adult morphological outcomes. However, much of the current experimental knowledge regarding dietary effects on masticatory form is derived from studies in which individuals are fed a non-variable diet for the duration of their postweaning growth period. Thus, it remains unclear how intra-individual variation in diet, due to ontogenetic variation in feeding behaviors or seasonal resource fluctuations, affects the resulting adult morphology. Furthermore, the mandible is composed of multiple developmental and functional subunits, and the extent to which growth and plasticity among these modules is correlated may be misestimated by studies that examine non-variable masticatory function in adults only. To address these gaps in our current knowledge, this study raised Sprague Dawley rats (n=42) in four dietary cohorts from weaning to skeletal maturity. Two cohorts were fed a stable ("annual") diet of either solid or powdered pellets. The other two cohorts were fed a variable ("seasonal") diet consisting of solid/powdered pellets for the first half of the study, followed by a shift to the opposite diet. Results of longitudinal morphometric analyses indicate that variation in the mandibular corpus is more prominent at immature ontogenetic stages, likely due to processes of dental eruption and the growth of tooth roots. Furthermore, adult morphology is influenced by both masticatory function and the ontogenetic timing of this function, e.g., the consumption of a mechanically resistant diet. The morphology of the coronoid process was found to separate cohorts on the basis of their early weanling diet, suggesting that the coronoid process/temporalis muscle module may have an early plasticity window related to high growth rates during this life stage. Conversely, the morphology of the angular process was found to be influenced by the consumption of a mechanically resistant diet at any point during the growth period, but with a tendency to reflect the most recent diet. The prolonged plasticity window of the angular process/pterygomasseteric muscle module may be related to delayed ossification and muscular maturation within this module. The research presented here highlights the importance of more naturalistic models of mammalian feeding, and underscores the need for a better understanding of the processes of both morphological and behavioral maturation that follow weaning.

Energetics of feeding, social behavior, and life history in non-human primates

Energy is a variable of key importance to a wide range of research in primate behavioral ecology, life history, and conservation. However, obtaining detailed data on variation in energetic condition, and its biological consequences, has been a considerable challenge. In the past 20years, tremendous strides have been made towards non-invasive methods for monitoring the physiology of animals in their natural environment. These methods provide detailed, individualized data about energetic condition, as well as energy allocations to growth, reproduction, and somatic health. In doing so, they add much-needed resolution by which to move beyond correlative studies to research programs that can discriminate causes from effects and disaggregate multiple correlated features of the social and physical environment. In this review, I describe the conceptual and methodological approaches for studying primate energetics. I then discuss the core questions about primate feeding ecology, social behavior, and life history that can benefit from physiological studies, highlighting the ways in which recent research has done so. Among these are studies that test, and often refute, common assumptions about how feeding ecology shapes primate biology, and those that reveal proximate associations between energetics and reproductive strategies.

Energetics of feeding, social behavior, and life history in non-human primates

Energy is a variable of key importance to a wide range of research in primate behavioral ecology, life history, and conservation. However, obtaining detailed data on variation in energetic condition, and its biological consequences, has been a considerable challenge. In the past 20years, tremendous strides have been made towards non-invasive methods for monitoring the physiology of animals in their natural environment. These methods provide detailed, individualized data about energetic condition, as well as energy allocations to growth, reproduction, and somatic health. In doing so, they add much-needed resolution by which to move beyond correlative studies to research programs that can discriminate causes from effects and disaggregate multiple correlated features of the social and physical environment. In this review, I describe the conceptual and methodological approaches for studying primate energetics. I then discuss the core questions about primate feeding ecology, social behavior, and life history that can benefit from physiological studies, highlighting the ways in which recent research has done so. Among these are studies that test, and often refute, common assumptions about how feeding ecology shapes primate biology, and those that reveal proximate associations between energetics and reproductive strategies.

An examination of factors potentially influencing birth distributions in golden snub-nosed monkeys (Rhinopithecus roxellana)

Many species of primates are considered seasonal breeders, but the set of factors, such as food availability, day length and temperature, that influence the timing of reproductive events for both wild and captive individuals remains unclear. Here, we examine the role of factors in shaping breeding patterns in Rhinopithecus roxellana, a temperate colobine primate. We used circular statistics to describe and compare the patterns of reproductive seasonality among individuals in 13 captive groups and two free ranging but provisioned groups at various locations throughout China. Almost 90% of births occurred in March, April and May in adult females residing in both free ranging (n = 131) and captive groups (n = 407). Births occurred principally in 2-4 months prior to the peak of food availability, while conceptions occurred in 1-2 months after the peak of food availability in free ranging but provisioned groups. Day length (latitude) had a significant effect on the timing of reproduction. However, females that experienced a wide variation of temperature between the lowest and highest monthly average temperature had a later conception date. These results support that day length and temperature might be factor influencing the timing of reproductive activity.

Seasonality of reproductive events and early mortality in a colony of hamadryas baboons (Papio hamadryas hamadryas) over a 30-year period: Capital breeding and life history patterns in a food-provisioned population seasonally thermally stressed

In environments where energy demands and resource availability vary seasonally, individuals are expected to time the optimal allocation of resources to support survival and reproduction. Although female baboons are regarded as all year round, capital breeders, we wondered how they would respond in an ecological scenario where food were not limiting, foraging effort were negligible, and they were thermally stressed during the cold winter. This study analyzes a 30-year database of conceptions, births, resumptions of postlactational ovarian activity, menarches, and prenatal and early postnatal reproductive failures recorded in a food-provisioned colony of hamadryas baboons located in a temperate zone (40°25'N) to search for seasonal patterns in their life-history patterns and explore its fitness consequences. The results show that the study females exhibited moderate seasonality and behaved like capital breeders; ovarian activity peaked during the period of benign weather conditions (spring and early summer) and births and lactation peaked during the period when they were thermally stressed and faced a negative energy balance (winter). Mistimed conceptions were more likely to fail than timed conceptions were, although this association could be artefactual due to the difficulty to accurately detect prenatal losses. Insolation and, to a lesser extent, temperature were positively associated with conceptions, resumptions of postlactational ovarian activity and onsets of menarche, and negatively associated with births. These findings highlight the extent of plasticity (width of peaks) and resiliency (retention of a capital breeding tactic even under highly seasonally thermally stressful cold conditions) in how primates can adjust their life history patterns and solve tradeoffs in a scenario of strong seasonal variation. Am. J. Primatol. 78:1149-1164, 2016. © 2016 Wiley Periodicals, Inc.

Are Humans Seasonally Photoperiodic?

Humans exhibit seasonal variation in a wide variety of behavioral and physiological processes, and numerous investigators have suggested that this might be because we are sensitive to seasonal variation in day length. The evidence supporting this hypothesis is inconsistent. A new hypothesis is offered here—namely, that some humans indeed are seasonally photoresponsive, but others are not, and that individual variation may be the cause of the inconsistencies that have plagued the study of responsiveness to photoperiod in the past. This hypothesis is examined in relation to seasonal changes in the reproductive activity of humans, and it is developed by reviewing and combining five bodies of knowledge: correlations of human birthrates with photoperiod; seasonal changes in the activity of the neuroendocrine pathway that could link photoperiod to gonadal steroid secretion in humans; what is known about photoperiod, latitude, and reproduction of nonhuman primates; documentation of individual variation in photoresponsiveness in rodents and humans; and what is known about the evolutionary ecology of humans.

When Love Is in the Air: Understanding Why Dogs Tend to Mate when It Rains

Seasonality of reproduction is observed in many species of organisms, across taxa, and is influenced by both biotic and abiotic factors. While such seasonality is easy to understand in temperate species exposed to extreme climates, it is more difficult to explain in the tropics. In many tropical species offspring are born during the season of high precipitation, which also coincides with high resource availability. Interestingly, in India, free-ranging dogs seem to mate, and not whelp, when it rains—an observation that cannot be explained by the resource abundance hypothesis. We carried out an extensive study to identify the mating seasons of free-ranging dogs, and observed a strong correlation between both the incidence and frequency of mating related behaviours of dogs, and precipitation levels. There are two clear mating seasons, of which the primary mating season coincides with the monsoon (rainy season) and the secondary mating season coincides with the nor’westerlies in this part of India. We speculate that this strong correlation is an effect of chemistry, rather than biology. While male dogs can mate round the year, females come into estrous seasonally. In the urban environment, dogs are exposed to a lot of olfactory noise, which can dilute the signal present in sex pheromones of the females in heat. A shower leads to increased humidity and reduced temperature of the air, leading to intensification of pheromone signals that trigger a sexual response in the dogs.

Assessment of the reproductive physiology of the potto (Perodicticus potto) through fecal hormone metabolite analyses and trans-abdominal ultrasonography

Potto (Perodicticus potto) reproductive biology has been minimally studied. Noninvasive endocrinology and ultrasonography are proven tools for reproductive assessment in other primates. In this study, we used fecal hormone metabolite analysis to monitor one adult male potto and four females at different life stages. Validated testosterone (T), estrone conjugate (EC), and progesterone (P4) enzyme immunoassays (EIA) were used to assess male testicular function and female ovarian and placental activity. The male excreted mean T concentrations of 4.72 (±1.66) μg/g feces, that did not differ (P > 0.05) over time or when paired with alternate females. Baseline concentrations of EC (range: 47.93-78.81 ng/g feces) and P4 (range: 2.29-12.46 μg/g feces) differed among adult females. Follicular phases averaged 9.1 days (±3.43, n = 30 phases), whereas luteal phases averaged 19.89 days (±9.49, n = 19 phases). Gestation length (n = 2 pregnancies) was 170 days. Gestational EC and P4 concentrations were positively correlated (pregnancy A, r (132) = 0.71; pregnancy B, r (145) = 0.76) and returned to non-pregnant luteal phase levels 3-7 days post parturition. Extreme differences between pregnant and non-pregnant EC and P4 concentrations may allow for one-sample pregnancy diagnosis. Trans-abdominal ultrasonography was validated for pregnancy diagnosis with the fetus observed between 100 and 110 days post breeding. To our knowledge, this is the first use of fecal endocrinology and ultrasonography to monitor reproductive function and pregnancy in this species, and the only study in any lorisid to measure progestagens in correlation with reproductive events.

Effect of photoperiod on characteristics of semen obtained by electroejaculation in stump-tailed macaques (Macaca arctoides)

Some environmental variables determining seasonal reproduction in mammals are temperature, humidity, food availability, and photoperiod. Among these, photoperiod is considered the main regulator of primates' seasonal reproduction, thus the latitudinal distribution of primate populations is a key factor determining the appearance of seasonal reproduction. The present work presents supporting discrete seasonality in male stump-tailed macaques (Macaca arctoides). We investigated whether semen quality and testosterone covaried with Mexico City's photoperiod and relative humidity by analyzing variations in the portions that form the ejaculate: the seminal liquid, the seminal coagulum, and the copulatory plug. Five male adult stump-tailed macaques were electroejaculated once a month, obtaining three semen samples per male, from August 2011 to July 2012 (except for December 2011) (n = 165). Our results showed that stump-tailed macaque sperm counts were significantly different between the portions of the ejaculate. The seminal coagulum contained the significantly largest number of spermatozoids, followed by the copulatory plug and the seminal fluid. Photoperiod and relative humidity had major influence on the sperm count in the seminal coagulum and the testosterone concentrations. Testosterone reached its highest values around the time when days and nights lasted the same hours, decreasing when days either grew longer or became shorter. Concerning relative humidity, sperm counts in the seminal coagulum were highly variable on dry days, but decreased as the relative humidity increased. We conclude that stump-tailed macaques have a discrete seasonality, occurring in spring and fall when macaques' reproductive condition and readiness for postcopulatory intrasexual competition increase.

Reassessing the determinants of breeding synchrony in ungulates

Predicting the consequences of climate change is a major challenge in ecology and wildlife management. While the impact of changes in climatic conditions on distribution ranges has been documented for many organisms, the consequences of changes in resource dynamics for species' overall performance have seldom been investigated. This study addresses this gap by identifying the factors shaping the reproductive synchrony of ungulates. In temporally-variable environments, reproductive phenology of individuals is a key determinant of fitness, with the timing of reproduction affecting their reproductive output and future performance. We used a satellite-based index of resource availability to explore how the level of seasonality and inter-annual variability in resource dynamics affect birth season length of ungulate populations. Contrary to what was previously thought, we found that both the degree of seasonal fluctuation in resource dynamics and inter-annual changes in resource availability influence the degree of birth synchrony within wild ungulate populations. Our results highlight how conclusions from previous interspecific analyses, which did not consider the existence of shared life-history among species, should be treated with caution. They also support the existence of a multi-faceted link between temporal variation in resource availability and breeding synchrony in terrestrial mammals, and increase our understanding of the mechanisms shaping reproductive synchrony in large herbivores, thus enhancing our ability to predict the potential impacts of climate change on biodiversity.

Seasonality of reproduction of wild black-and-white snub-nosed monkeys (Rhinopithecus bieti) at Mt. Lasha, Yunnan, China

Black-and-white snub-nosed monkeys (Rhinopithecus bieti) inhabit one of the harshest habitats by any nonhuman primate. Reliable predictive cues to initiate reproduction may be particularly critical for R. bieti because they inhabit such seasonally energetically challenging environments. To better understand the seasonal distribution of and predictive cues to reproduction, we collected breeding and birth data in a population of R. bieti at Mt. Lasha in Yunling Nature Reserve, Yunnan, China, from January 2008 to May 2010, using a combination of 10-min instantaneous scans and ad libitum observations. We examined variations in temperature, rainfall, and food availability, as well as photoperiod differences between Mt. Lasha and the more northerly Xiaochangdu to identify environmental influences on the timing of reproductive events. Our data show the area exhibited distinct seasonal fluctuations in rainfall, temperature, and food availability. Mating occurred year-round, but peaked in August, coinciding with the end of the period of highest temperatures and food availability, and during the peak rainfall. Copulation frequency peaked 1 month after corresponding peaks in staple foods, rainfall, and minimum temperatures, and 3-4 months after peaks in high-quality foods. Births were significantly seasonal, with a birth peak from mid-February to early April, and a mean birth date of 14 March. Eleven births occurred in 41 days in 2009, and 16 births occurred in 52 days in 2010. Births occurred during periods of increasing temperatures and food availability. Our findings are suggestive of at least one environmental control of conception timing, and support the notion that food availability during key reproductive stages is an ultimate factor for birth seasonality, but provide no supporting evidence for photoperiod during the conception season as a proximate cue to reproduction in R. bieti.

Rensch's rule, Bergmann's effect and adult sexual dimorphism in wild monogamous owl monkeys (Aotus azarai) of Argentina

Some monogamous primates are characterized by biparental care, territoriality, and a reduced level of physical dimorphism. In others, the relationship between those behavioral patterns and dimorphism is less clear. I tested Bergmann's and Rensch's rules using Aotus spp. body mass data and I characterized the extent of sexual dimorphism in body mass, dental and physical measurements in a socially monogamous owl monkey population (n = 91 adults) from the Argentinean Gran Chaco. A. azarai azarai from the Argentinean Chaco is larger than the more tropical owl monkey species (r = 0.7, N = 6 species), but there is no apparent increase in sexual dimorphism with increased body mass. The body masses of adult male and female A. a. azarai were remarkably similar (Mean = 1.26 kg); there were no marked sex differences in most skeletal measurements, but males had higher and wider upper and lower canines than did females. Body mass and neck circumference were positively and strongly related (r = 0.533, n = 52), and the body mass of adults was not a reliable indicator of their age (r = 0.03, n = 10). The data illustrate the complexities inherent in examining and summarizing within population variation in skeletal and nonskeletal measurements and contribute to a better understanding of the relationships between monogamous behavioral patterns and sexual dimorphism.