Lifetime reproductive output and life-history traits of lizards

Aim: Latitudinal gradients in life-history traits are apparent in
many taxa and are expected to be strong for ectotherms that have
temperature-driven constraints on performance and fitness. The strength of
these gradients, however, should also be affected by diet. Because diet
type (carnivory, omnivory, herbivory) influences accessibility to
nutrition and assimilation efficiency, we aim to study how diet affects
latitudinal gradients in lifetime reproductive output and the underlying
life-history traits in ectotherms. Location: Global. Time
period: Recent. Major taxa studied: Lizards (Reptilia,
Squamata, Sauria). Methods: We used empirical (352 species) and
phylogenetically imputed data (563 species) to analyse the interactive
effects of latitude and diet on life-history traits (longevity, age at
maturity, reproductive lifespan, hatchling mass, clutch/brood size,
clutch/brood frequency, female mass) and lifetime reproductive output of
lizards. Results: Lifetime reproductive output does not
significantly differ in lizards across diet types, and only carnivores
exhibit a small increase at higher latitudes. Diet type, however,
influences latitudinal patterns of individual life-history traits.
Carnivores exhibit a shift towards “slower-paced” life-histories at higher
latitudes for most traits (increased longevity, age at maturity,
reproductive lifespan, and decreased clutch frequency). By contrast,
herbivores either display “faster-paced” life-histories (reduction in
reproductive lifespan, hatchling mass, female mass) or no change (clutch
frequency, clutch size, age at maturity) at higher latitudes. Omnivores
exhibit intermediate and muted latitudinal patterns. Main
conclusions: We suggest that the nutritional challenges of
herbivory, compounded by thermal constraints at higher latitudes, may
explain differences in life-history characteristics of herbivorous
ectotherms. Intermediate patterns exhibited by omnivores highlight how
flexibility in diet can buffer environmental challenges at higher
latitudes. Our results indicate that lizards with different diet types
display various trends in their life-histories across latitudes, which
eventually balance out to result in similar reproductive outputs
throughout their lifetime, with little benefits to carnivory.