Individual quality and age but not environmental or social conditions modulate costs of reproduction in a capital breeder

Abstract

Costs associated with reproduction are widely known to play a role in the evolution of reproductive tactics with consequences to population and eco‐evolutionary dynamics. Evaluating these costs as they pertain to species in the wild remains an important goal of evolutionary ecology. Individual heterogeneity, including differences in individual quality (i.e., among‐individual differences in traits associated with survival and reproduction) or state, and variation in environmental and social conditions can modulate the costs of reproduction; however, few studies have considered effects of these factors simultaneously. Taking advantage of a detailed, long‐term dataset for a population of feral horses (Sable Island, Nova Scotia, Canada), we address the question of how intrinsic (quality, age), environmental (winter severity, location), and social conditions (group size, composition, sex ratio, density) influence the costs of reproduction on subsequent reproduction. Individual quality was measured using a multivariate analysis on a combination of four static and dynamic traits expected to depict heterogeneity in individual performance. Female quality and age interacted with reproductive status of the previous year to determine current reproductive effort, while no effect of social or environmental covariates was found. High‐quality females showed higher probabilities of giving birth and weaning their foal regardless of their reproductive status the previous year, while those of lower quality showed lower probabilities of producing foals in successive years. Middle‐aged (prime) females had the highest probability of giving birth when they had not reproduced the year before, but no such relationship with age was found among females that had reproduced the previous year, indicating that prime‐aged females bear higher costs of reproduction. We show that individual quality and age were key factors modulating the costs of reproduction in a capital breeder but that environmental or social conditions were not, highlighting the importance of considering multiple factors when studying costs of reproduction.

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

“…Reproduction is a costly process [ 1 – 4 ] and is directly linked to the evolution of reproductive strategies [ 5 ] and population dynamics [ 6 ]. In female mammals, reproduction is the most energetically demanding life-history phase [ 7 ], so it is firmly regulated by body condition and food availability [ 8 ].…”

Age-specific effects of density and weather on body condition and birth rates in a large herbivore, the Przewalski’s horse

“…As discussed above, young female horses still need to allocate energy into their own growth until an age of around 4 years (Csurhes et al 2016 ), and thus the energetic investment of young mothers into reproduction can be proportionally higher compared to older and fully grown females, possibly leading to higher reproductive fitness costs in young mothers. This hypothesis finds further support by a study on a feral horse population on an island in Nova Scotia, Canada, showing that low quality females carried the highest costs of reproduction in terms of a notably reduced foaling probability during the subsequent season (Debeffe et al 2017 ). Horses, as capital breeders, can hardly compensate for a lack of energy during current reproduction via an increased food intake, which can typically lead to such delayed effects of low body condition on reproductive performance (Jönsson 1997 ).…”

Quantitative genetics of gastrointestinal strongyle burden and associated body condition in feral horses

“…First, traits closely linked with fitness are expected to have lower heritability as strong selection erodes variance (Merilä and Sheldon, 1999). Condition is often used as a proxy for fitness (Barnett et al, 2015) and, as a component of individual quality in Sable Island horses, condition has been shown to link with reproductive success (Debeffe et al, 2017). Therefore, it is possible that strong selection imposed by the harsh conditions on Sable Island has eroded the additive genetic variance for body condition in this population.…”