Limoilou-Amélie Renaud’s research while affiliated with Université du Québec en Abitibi-Témiscamingue and other places

Long-term fitness effects of parental age could affect population dynamics, as age structure can vary considerably over time. Few studies of wild animals, however, have examined the possible long-term fitness consequences of parental age. Based upon 50 years of data on wild bighorn sheep, we investigated how parental age affected three offspring traits – mass at three years, longevity, and female lifetime reproductive success. We also tested for a survival filter which could mask or increase fitness effects of parental age. Our results showed a significant, quadratic negative association between maternal age, offspring longevity and female lifetime reproductive success. Offspring born to mothers aged 5-6 years lived about 2 years longer and weaned about 1.5 lambs more than siblings born to mothers aged 12-13 years. The effect of paternal age was not significant. There was also a positive association between the longevity of mothers and offspring. We did not detect any effects of parental age on mass at three years for offspring of either sex. These results demonstrate the presence of persistent maternal age effects in a long-lived species. The sex-specific effects support the importance of analyzing maternal and paternal age effects separately, as well as effects on female and male offspring. This study advances our understanding of evolutionary processes and population dynamics in wild long-lived mammals.

Beluga (Delphinapterus leucas) from the St. Lawrence Estuary, Canada, have been declining since the early 2000s, suggesting recruitment issues as a result of low fecundity, abnormal abortion rates or poor calf or juvenile survival. Pregnancy is difficult to observe in cetaceans, making the ground truthing of pregnancy estimates in wild individuals challenging. Blubber progesterone concentrations were contrasted among 62 SLE beluga with a known reproductive state (i.e. pregnant, resting, parturient and lactating females), that were found dead in 1997 to 2019. The suitability of a threshold obtained from decaying carcasses to assess reproductive state and pregnancy rate of freshly-dead or free-ranging and blindly-sampled beluga was examined using three statistical approaches and two data sets (135 freshly harvested carcasses in Nunavik, and 65 biopsy-sampled SLE beluga). Progesterone concentrations in decaying carcasses were considerably higher in known-pregnant (mean ± sd: 365 ± 244 ng g−1 of tissue) than resting (3.1 ± 4.5 ng g−1 of tissue) or lactating (38.4 ± 100 ng g−1 of tissue) females. An approach based on statistical mixtures of distributions and a logistic regression were compared to the commonly-used, fixed threshold approach (here, 100 ng g−1) for discriminating pregnant from non-pregnant females. The error rate for classifying individuals of known reproductive status was the lowest for the fixed threshold and logistic regression approaches, but the mixture approach required limited a priori knowledge for clustering individuals of unknown pregnancy status. Mismatches in assignations occurred at lipid content < 10% of sample weight. Our results emphasize the importance of reporting lipid contents and progesterone concentrations in both units (ng g−1 of tissue and ng g−1 of lipid) when sample mass is low. By highlighting ways to circumvent potential biases in field sampling associated with capturability of different segments of a population, this study also enhances the usefulness of the technique for estimating pregnancy rate of free-ranging population.

Marine mammal populations worldwide greatly benefitted from conservation measures put in place since the 1970s following overexploitation, and many pinniped populations have recovered. However, threats due to bycatch, interspecific interactions or climate change remain, and detailed knowledge on vital rates, population dynamics, and their responses to environmental changes is essential for efficient management and conservation of wild populations. In this study, we quantified pup abundance and survival of individually marked harbour seal (Phoca vitulina Linnaeus, 1758) pups during the preweaning period at Bic Island and Métis sites in the St. Lawrence Estuary from 1998 to 2019. We used mark-recapture models to evaluate competing hypotheses regarding variation in daily preweaning survival rates and capture probability during the pups’ first 30 days of life. Pup abundance increased from 76 [95% CI: 59, 101] to 323 [95% CI: 233, 338] in the past two decades at Bic Island and from 66 [95% CI: 47, 91] to 285 [95% CI: 204, 318] at Métis. Preweaning survival was generally higher at Bic (0.73 [95% CI: 0.58, 0.82]) than at Métis (0.68 [95% CI: 0.52, 0.79]). We hypothesize that differences between habitats and human disturbance contribute to lower preweaning survival at Métis, but behavioural studies are needed to understand the impacts of disturbance on mother–pup interactions during the nursing period.

Phenological changes in response to climate change have been documented across taxa throughout the Northern Hemisphere. The rate of advancement often decreases with increasing trophic level, resulting in mismatch between consumers and their resources. The match-mismatch hypothesis has been investigated in bighorn sheep (Ovis canadensis) at Ram Mountain, Alberta (52ºN, 115ºW), a population which has been monitored since 1971. The gestation period of bighorn sheep is 172 ± 2 days, and our team previously showed that ewes have plastically responded to environmental changes in fall by advancing their conception date and giving birth on average 15 days earlier in recent years. However, spring conditions have changed at a much faster rate, resulting in lambs being born an average of 10 days later with respect to spring green-up. Ewes do not seem to pass on costs of mismatch onto lambs, leading us to hypothesize that mismatch may increase maternal reproductive costs. Our goal was to determine whether maternal summer mass gain is affected by increasing mismatch. We use parturition dates recorded since 1992, and spring green-up dates obtained from the Enhanced Vegetation Index available since 2000, to test the effects of phenological mismatch on bighorn ewe summer mass gain. A total of 152 females were measured, between 1-11 times each, with a total of 449 parturition dates recorded since 1992, 279 of which have been recorded since 2000. Mismatch between spring green-up and parturition, (parturition date - green-up date, in Julian days) ranges from -24 days (early parturition) to +120 days (late parturition), and population mismatch, (individual parturition date - population median parturition date, in Julian days), ranges from -18 to +95 days. Preliminary results indicate that ewes with a greater positive mismatch, both green-up and population, gain less mass over summer; those with the greatest mismatch gain up to 6kg less during summer than those whose parturition dates are matched with spring green-up or median parturition date. This suggests that ewes who are missing the highest quality forage have the greatest reproductive cost, using their fat reserves for lactation. Current knowledge of the effects of climate change on phenological plasticity are primarily from studies on birds, which are income breeders and thus more sensitive to daily changes in food abundance. This study improves our understanding of large mammal phenological plasticity, and the potential costs of phenological mismatch, which are expected to increase with climate change.

In species with long gestation, females commit to reproduction several months before parturition. If cues driving conception date are uncoupled from spring conditions, parturition could be mistimed. Mismatch may increase with global change if the rate of temporal changes in autumn cues differs from the rate of change in spring conditions. Using 17 years of data on climate and vegetation phenology, we show that autumn temperature and precipitation, but not vegetation phenology, explain parturition date in bighorn sheep. Although autumn cues drive the timing of conception, they do not predict conditions at parturition in spring. We calculated the mismatch between individual parturition date and spring green‐up, assessed whether mismatch increased over time and investigated the consequences of mismatch on lamb neonatal survival, weaning mass and overwinter survival. Mismatch fluctuated over time but showed no temporal trend. Temporal changes in green‐up date did not lead to major fitness consequence of mismatch. Detailed data on individually marked animals revealed no effect of mismatch on neonatal or overwinter survival, but lamb weaning mass was negatively affected by mismatch. Capital breeders might be less sensitive to mismatch than income breeders because they are less dependent on daily food acquisition. Herbivores in seasonal environments may access sufficient forage to sustain lactation before or after the spring ‘peak’ green‐up, and partly mitigate the consequences of a mismatch. Thus, the effect of phenological mismatch on fitness may be affected by species life history, highlighting the complexity in quantifying trophic mismatches in the context of climate change.

Public outreach on actual issues in ecology

Understanding how spring phenology influences early life can provide important insights into drivers of future development and survival. We combined unique, long-term data from a bighorn sheep population and satellite-derived phenology indices to quantify the relative importance of maternal and environmental influences on milk composition and lamb overwinter survival. Based on 216 milk samples from 34 females monitored over 6 years, we found that longer snow-free and vegetation growing seasons increased milk fatty acid, iron and lactose concentrations. Structural equation modelling revealed no causality between milk energy content, lamb weaning mass and lamb overwinter survival. Our results suggest that spring conditions can affect milk energy content, but we did not detect any effect on lamb overwinter survival either directly or indirectly through lamb weaning mass. The effect of green-up date on milk composition and energy content suggests that herbivores living in seasonal environments, such as the bighorn sheep, might rely on a strategy intermediate between ‘capital’ and ‘income’ breeding when energy demands are high.