Body size constrains maternal investment in a small sea turtle species

Abstract

To maximise reproductive fitness, species make trade-offs among reproductive traits, e.g., offspring quantity vs. offspring size, within energetic, anatomical, and physiological constraints. Sea turtles are a model taxon to study reproductive trade-offs, because they lack parental care and because there are strong selective pressures on hatchlings due to high predation rates. Natural selection therefore typically favours optimising offspring size over offspring quantity. Nevertheless, the balance between these traits varies between both sea turtle populations and species. Here, we quantified individual variation in reproductive traits of olive ridley turtles (Lepidochelys olivacea) in northwest Costa Rica. Olive ridley females displayed considerable inter-female variation in reproductive traits with larger females producing larger clutches. These larger females also produced longer and heavier hatchlings than smaller females despite producing similar sized eggs. Females did not exhibit a trade-off between clutch size and egg mass, although variation in clutch size (coefficient of variation = 16.8%) was greater than that of egg mass (10.1%). Producing more eggs per clutch had 1.8 times the effect of producing heavier eggs at increasing clutch mass. The effect of clutch frequency was 2.5 times that of clutch size on seasonal egg production and 2.4 times that of clutch size on seasonal hatchling production. In conclusion, olive ridley turtles exhibit considerable variation in reproductive traits, but their small body size constrains clutch size and has implications for their overall reproductive output.