Abstract
Based on 20,000 records representing c. 11,000 individuals from an 8-year capture-mark-recapture (CMR) study, we tested and confirmed a new case of invariant clutch size (ICS) in a sexually dichromatic lacertid lizard, Takydromus viridipunctatus. In the grassland habitat of the early succession stage, females showed strictly low and invariant clutch size, multiple clutches in a breeding season, high reproductive potential, and annual breeding cycles that correspond to the emergence of male courtship coloration. The hatchlings mature quickly, and join the adult cohort for breeding within a few months, whereas adults show low survival rates and a short lifespan, such that most die within one year. Mortality increased in both sexes during the breeding season, especially in females, indicating an unequal cost of reproduction in survival. These life history characters may be explained by two non-exclusive hypotheses of ICS—arboreal hypothesis and predation hypothesis—within the ecological context of their habitat. Our study highlights a confirmed case of ICS, which adapts well to this r-selected grassland habitat that experiences seasonal fluctuation and frequent disturbance.
Highlights
Life history traits and reproductive strategies are keys to our understanding of demographic processes and population dynamics in ecological studies
The monthly survival rate yielded to an annual survival rate less than 0.1, suggesting the low survival rate of this lizard compared to most other Squamata [21]
The high predation risk on adult lizards has been regarded as a selection for early reproduction [37, 38], which further leads to small maturity size, small clutch size because of body constraint, and multiple clutch per season [9, 15]
Summary
Life history traits and reproductive strategies are keys to our understanding of demographic processes and population dynamics in ecological studies. Natural selection predicts that organisms should optimize the timing of reproduction (e.g. age or season) and the number of offspring in a single reproductive event (e.g. clutch size) in order to maximize their fitness [1,2,3]. The tradeoff between survival and reproduction under resource limitation, known as “cost of reproduction” [5,6,7], is dynamic and can differ significantly across species and ecosystems, leading to variation in the optimized clutch size. Variation in clutch size for VCS species is usually conditiondependent, influenced by intrinsic factors such as age, body size, or nutrition condition, and/or external factors such as resource abundance [6, 8,9,10]. ICS independently evolved several times in lizards, and is widespread among anoles [13] and gekkotan [14] lizards
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