Contrasting the Effects of Maternal and Behavioral Characteristics on Fawn Birth Mass in White-Tailed Deer

Influences of Maternal Weight and Geographic Factors on Offspring Traits of the Edible Dormouse in the NE of the Iberian Peninsula

The main goal of this study was to analyze the reproductive patterns of edible dormouse (Glis glis) populations in the northeast of the Iberian Peninsula using an 18-year period of data obtained from nest boxes collected between 2004 and 2021. The average litter size in Catalonia (Spain) was 5.5 ± 1.60 (range: 2-9, n = 131), with litter sizes between 5 and 7 pups as the more frequent. The overall mean weight in pink, grey and open eyes pups was 4.8 g/pup, 11.7 g/pup and 23.6 g/pup, respectively. No differences in offspring weights between sexes were found in any of the three age groups. Maternal body weight was positively associated with mean pup weight, whereas no correlation between the weight of the mothers and litter size was found. The trade-off between offspring number and size was not detected at birth. Regarding litter size variation across the geographic gradient (and their climatic gradient associated) from the southernmost populations of the Iberian Peninsula located in Catalonia to the Pyrenees region in Andorra, no evidence to suggest that geographic variables affect litter size was found, discarding (1) an investment in larger litters to compensate shorter seasons related to higher altitudes or northern latitudes, and (2) variation in litter size related to weather changes (e.g., temperature and precipitation) along latitudinal and/or altitudinal gradients.

Maternal effects on reproduction in the precocial European hare (Lepus europaeus)

In female mammals, reproduction, and in particular lactation, is the energetically most exigent life-history phase. Reproduction is strongly controlled by body reserves and food availability, so females with better body condition or food supply are believed to have higher reproductive output. Additionally, the growth and mortality of young mammals depends on their postnatal development. Therefore, the degree of precociality affects energetic demands for both mothers and young. To study the reproductive performance of the precocial European hare (Lepus europaeus), we analysed relationships between six predictor variables describing maternal and environmental effects and nine response variables relating to reproduction from 217 captive females. We compared the data with those of precocial and altricial mammal species from an extensive literature search. For hares, we found: (1) Heavier females had heavier litters at birth. (2) In summer and spring, total litter mass was larger than in winter. (3) At the end of lactation, the litters of multiparous females were heavier than those of primiparous females. (4) Both older females and females giving birth for the first time had relatively high leveret mortality during lactation. Comparing our results with the literature for other mammals revealed that the body condition (i.e., body mass) of females before birth is predictive of reproductive parameters in both precocial and altricial species. In the precocial hare, female body condition is no longer predictive of reproductive parameters at the end of lactation, whereas in altricial species, female body condition remains predictive of reproduction (litter mass at the end of lactation, offspring mortality) until the end of lactation. We conclude that these effects are caused by precocial offspring feeding on solid food soon after birth and, thus, being less dependent on the mother's body condition during lactation than altricial offspring. In line with this, precociality might have evolved as a way of buffering offspring against maternal effects.

Behavioral plasticity mitigates the effect of warming on white-tailed deer

Climate change is expected to create novel environments in which extant species cannot persist, therefore leading to the loss of them and their associated ecological functions within the ecosystem. However, animals may employ behavioral mechanisms in response to warming that could allow them to maintain their functional roles in an ecosystem despite changed temperatures. Specifically, animals may shift their activity in space or time to make use of thermal heterogeneity on the landscape. However, few studies consider the role of behavioral plasticity and spatial or temporal heterogeneity in mitigating the effects of climate change. We conducted experiments to evaluate the potential importance of behavior in mediating the net effects of warming on white-tailed deer (Odocoileus virginianus). We used shade structures to manipulate the thermal environment around feeding stations to monitor deer feeding activity and measure total consumption. In individual experiments where deer only had access to unshaded feeders, deer fed less during the day but compensated by increasing feeding during times when temperature was lower. In group experiments where deer had access to both shaded and unshaded feeders, deer often fed during the day but disproportionally preferred the cooler, shaded feeders. Our results suggest that deer can capitalize on temporal and spatial heterogeneity in the thermal environment to meet nutritional and thermal requirements, demonstrating the importance of behavioral plasticity when predicting the net effects of climate change.

Body mass influences maternal allocation more than parity status for a long-lived cervid mother

Mothers should balance the risk and reward of allocating resources to offspring to optimize the reproductive value of both offspring and mother while maximizing lifetime reproductive success by producing high-quality litters. The reproductive restraint hypothesis suggests maternal allocation should peak for prime-aged mothers and be less for younger mothers such that body condition is not diminished to a level that would jeopardize their survival or future reproductive events. We assessed if reproductive tactics varied by maternal body mass and parity status in captive female white-tailed deer (Odocoileus virginianus) to determine if prime-aged mothers allocate relatively more resources to reproduction than primiparous mothers. Maternal body mass, not parity status, positively affected maternal allocation, with heavier mothers producing both heavy litters and heavy individual offspring. Conversely, maternal body mass alone did not affect litter size, rather the interaction between maternal body mass and parity status positively affected litter size such that maternal body mass displayed a greater effect on litter size for primiparous than multiparous mothers. Our results suggest that heavy white-tailed deer mothers allocate additional resources to current year reproduction, which may be an adaptation allowing mothers to produce high-quality litters and increase their annual reproductive success because survival to the next reproductive attempt is not certain.

Weather and landscape factors affect white-tailed deer neonate survival at ecologically important life stages in the Northern Great Plains

Offspring survival is generally more variable than adult survival and may limit population growth. Although white-tailed deer neonate survival has been intensively investigated, recent work has emphasized how specific cover types influence neonate survival at local scales (single study area). These localized investigations have often led to inconsistences within the literature. Developing specific hypotheses describing the relationships among environmental, habitat, and landscape factors influencing white-tailed deer neonate survival at regional scales may allow for detection of generalized patterns. Therefore, we developed 11 hypotheses representing the various effects of environmental (e.g., winter and spring weather), habitat (e.g., hiding and escape cover types), and landscape factors (e.g., landscape configuration regardless of specific cover type available) on white-tailed deer neonate survival up to one-month and from one- to three-months of age. At one-month, surviving fawns experienced a warmer lowest recorded June temperature and more June precipitation than those that perished. At three-months, patch connectance (percent of patches of the corresponding patch type that are connected within a predefined distance) positively influenced survival. Our results are consistent with white-tailed deer neonate ecology: increased spring temperature and precipitation are likely associated with a flush of nutritional resources available to the mother, promoting increased lactation efficiency and neonate growth early in life. In contrast, reduced spring temperature with increased precipitation place neonates at risk to hypothermia. Increased patch connectance likely reflects increased escape cover available within a neonate's home range after they are able to flee from predators. If suitable escape cover is available on the landscape, then managers could focus efforts towards manipulating landscape configuration (patch connectance) to promote increased neonate survival while monitoring spring weather to assess potential influences on current year survival.

Birth date promotes a tortoise or hare tactic for body mass development of a long-lived male ungulate

Maternal and early-life influences may affect life-long individual phenotype, potentially influencing reproductive success. However, some individuals may compensate for a poor start to life, which may improve longevity and reproductive success later in life. We developed four models to assess whether maternal characteristics (age, body mass and previous year cumulative lactation demand) and/or birth date influenced a long-lived mammal's phenotype to maturity. We used a directional separation analysis to assess the relative influence of each maternal characteristic and birth date on captive male white-tailed deer (Odocoileus virginianus) body mass and antler size. We found that birth date was the only characteristic that persistently influenced male body mass. Depending on when offspring were born, they used alternative tactics to increase their body mass. Birth date positively influenced body mass at 1, 2 and 3 years of age-indicating males displayed faster growth and compensated for late birth (hare tactic). However, early-, heavy-born males were heavy juveniles, and juvenile body mass positively influenced mature body mass (slow but steady growth; tortoise tactic). Our findings provide a first evidence that a long-lived ungulate can display alternative tactics to achieve heavy body mass; individuals are either born early and heavy and are heavy throughout life (tortoise), or light, late-born individuals compensate for a poor start in life by growing at a faster rate to equal or surpass the body mass of early-born individuals (hare). Either tactic may be viable if it influences reproductive success as body mass positively influences access to mates in ungulates.