The evolution of reproductive strategies in turtles

Abstract

Optimal egg size theory assumes that changes in the egg and clutch are driven by selection, resulting in adjustments for the largest possible production of offspring with the highest fitness. Evidence supports the idea that large-bodied turtles tend to produce larger clutches with small and round eggs, while smaller species produce small clutches with large and elongated eggs. Our goals were to investigate whether egg and clutch size follow the predictions of egg size theory, if there are convergent reproductive strategies, and identify ecological factors that influence clutch and egg traits across all clades of living turtles. Using phylogenetic methods, we tested the covariance among reproductive traits, if they are convergent among different turtle lineages, and which ecological factors influence these traits. We found that both egg shape and size inversely correlate with clutch size, although with different evolutionary rates, following the predictions of the egg size theory. We also present compelling evidence for convergence among different turtle clades, over at least two reproductive strategies. Furthermore, climatic zone is the only ecological predictor to influence both egg size and fecundity, while diet only influences egg size. We conclude that egg and clutch traits in Testudines evolved independently several times across non-directly related clades that converged to similar reproductive strategies. Egg and clutch characteristics follow the trade-offs predicted by egg size theory and are influenced by ecological factors. Climatic zone and diet play an important role in the distribution of reproductive characteristics among turtles.

Reproductive Traits Demonstrate How Well the Mediterranean Stripe-Necked Turtle Mauremys leprosa Can Flourish under Highly Degraded–Polluted Conditions

“…Moreover, in the highly degraded–polluted habitat, egg length was constrained by clutch size, since they were negatively correlated. This result is consistent with the predictions from optimal egg and clutch size theory, which assume that large-bodied turtles tend to produce larger clutches with small eggs [ 49 , 60 , 61 ]. However, the correlations in the Spanish conspecific populations, as in the undisturbed habitat population of the present study, were not statistically significant [ 18 , 19 ].…”

“…Moreover, according to several studies, populations of the same taxa may also differ in their sizes at maturity and their growth when subjected to different environmental pressures [ 45 , 46 , 47 ]. The most involved biotic factors are variations in trophic resources [ 48 , 49 ], competition, and predation [ 50 , 51 ].…”

“…Enjoying the above described ability to adapt to a restrictive environment, the species monopolizes the resources of the water body and its supplies, taking advantage of the disappearance of competitors and predators, which have no comparable performance [ 13 , 14 , 17 ]. Jorgewich-Cohen et al [ 49 ] strongly implicated ecological factors, mainly resource availability on clutch capacity and egg size of chelonian species. The very wide food spectrum of M. leprosa (omnivory with a predominance of carnivory, but also scavenging and coprophagy) allows it to obtain supplies at will in eutrophic and polluted waters [ 8 , 13 , 52 ].…”

Home range of three turtle species in Central Yucatan. A comparative study

“…During the rainy season freshwater turtles mate and nest [ 47 ], as well as feed and store energy reserves for the next dry season and aestivation period [ 48 , 49 ]. As predicted, the three studied species moved longer distances during rainy season and were observed walking, in courtship, foraging, and basking.…”