In humans, pronounced age differences between parents have deleterious fitness consequences. In particular, the number of children is lower when mothers are much older than fathers. However, previous analyses failed to disentangle the influence of differential parental age from a direct age effect of each parent. In this study, we analyse the fitness consequences of both parental age and parental age differences on litter size and offspring survival in two closely related species of lemurs living in captivity. As captive lemurs do not choose their reproductive partner, we were able to measure litter size and offspring survival across breeding pairs showing a wide range of parental age differences. However, we demonstrated that the effect of the parental age difference on litter size was fully accounted for by female reproductive senescence because females mating with much younger males were old females. On the other hand, both parental age difference and female reproductive senescence influenced offspring survival. Our results emphasize the importance of teasing apart the effect of parental reproductive senescence when investigating the health and fitness consequences of parental age differences and also provide new insights for conservation programmes of endangered species.
The fish-to-tetrapod transition-followed later by terrestrialization-represented a major step in vertebrate evolution that gave rise to a successful clade that today contains more than 30,000 tetrapod species. The early tetrapod Ichthyostega was discovered in 1929 in the Devonian Old Red Sandstone sediments of East Greenland (dated to approximately 365 million years ago). Since then, our understanding of the fish-to-tetrapod transition has increased considerably, owing to the discovery of additional Devonian taxa that represent early tetrapods or groups evolutionarily close to them. However, the aquatic environment of early tetrapods and the vertebrate fauna associated with them has remained elusive and highly debated. Here we use a multi-stable isotope approach (δC, δO and δS) to show that some Devonian vertebrates, including early tetrapods, were euryhaline and inhabited transitional aquatic environments subject to high-magnitude, rapid changes in salinity, such as estuaries or deltas. Euryhalinity may have predisposed the early tetrapod clade to be able to survive Late Devonian biotic crises and then successfully colonize terrestrial environments.
Evolutionary theories of senescence predict that a high allocation to reproduction during early life should have long-term deleterious consequences on future reproduction or survival because individuals have to face an energy allocation trade-off between reproductive effort and the maintenance of body condition. Using a high-quality dataset from 1,721 red ruffed lemurs (RRL, Varecia rubra) and 3,637 black and white ruffed lemurs (BWRM, V. variegata) living in captivity, we tested the existence of a trade-off between reproductive effort and late-life survival after accounting for possible confounding effects of natal environmental conditions. We report clear evidence of actuarial senescence (i.e., the decline of annual survival with increasing age) in both sexes and for both species of ruffed lemurs. RRL had a lower baseline mortality and senesced faster than BWRL, resulting in similar distributions of longevities for both species. No between-sex difference was observed in any species. Lastly, a higher reproductive effort was positively associated with an increase of survival late in life, and thereby an increased longevity. These findings indicate that individual quality rather than trade-off drives the association between reproductive success and survival pattern among individual lemurs of both species in the protected environment provided by zoos. Lemurs are among the world's highest conservation priorities and better understanding factors influencing their longevity and actuarial senescence patterns should improve their conservation.
A fifth of all known species are currently classified as threatened in the wild: the rate of biodiversity loss is rapid, continuous, and mostly due to anthropogenic activities. To slow down this decline, the accurate estimation of demographic parameters for threatened species is critical. With this aim, zoo institutions play an important role, giving access to data on zoo-housed animals, which aids researchers working on species life-history traits and intrinsic factors influencing the fitness of both sexes, such as age. While tigers
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