Seasonal Changes in Food Quality: A Proximate Cue for Reproductive Timing in Marine Iguanas

Abstract

We investigated the proximate environmental cues that influence the timing of reproduction in the seasonally and synchronously breeding Galápagos marine iguana (Amblyrhynchus cristatus). Marine iguana foraging patterns are closely linked to the tidal cycle, and they feed exclusively on macroalgae. The Galápagos Islands are characterized by seasonal currents that impact water temperature and ultimately algal abundance, which is known to affect iguana body condition and survival. In our study, marine iguanas preferred Gelidium sp., which had the highest nutritional quality (nitrogen content, carbon content, and C:N ratio) of the three species of macroalgae on which they feed. Nutritional quality in Gelidium changed predictably with increasing sea surface temperature, peaking around the median iguana copulation date. Similarly, foraging behavior changed around the time copulations began. To test if consistent relationships existed among food quality, water temperature, and breeding life history, we used seven years of data from this population and found that breeding occurred earlier in years when the mean December sea surface temperature was warmer. Although iguanas might cue directly on changes in sea surface temperature, given the frequency and intensity of El Niñ o events in the Galápagos, this hypothesis is unlikely. Rather, our results suggest that marine iguanas may use subtle changes in food quality (particularly energy content) associated with seasonal, but annually variable, changes in water temperature as a cue to initiate breeding. The excess available energy may be used to withstand the costly breeding period, as well as to provision yolk to improve hatchling growth and survival.

Evolution of body size in Galapagos marine iguanas

“…In fact, recent reports from the Galapagos seem to support this prediction. Overall, the availability of food of high quality appears to be of such pervasive importance for marine iguanas that they precisely time their one annual reproductive season with minute changes in food quality (Rubenstein & Wikelski 2003). …”

Exploring the role of temperature in the ocean through metabolic scaling

“…While this could alter plant community composition (Lemoine et al 2014), the effect on standing plant biomass is unknown. Work in marine systems has focused on temperature-driven changes in macroalgal palatability (Sotka and Giddens 2009), nutritional quality (Rubenstein andWikelski 2003, Staehr andWernberg 2009), and chemical defenses (Sudatti et al 2011) in the presence and absence of herbivores.…”

Approximation of a physiologically structured population model with seasonal reproduction by a stage-structured biomass model

“…In the model, reproduction is assumed to be an externally forced, seasonal event that occurs simultaneously for all mature individuals. Timing of spawning has been associated with seasonal external cues such as day length, food quality, humidity, solar insolation, and temperature (Bromage et al 2001;Rubenstein and Wikelski 2003;Brown and Shine 2006;van Woesik et al 2006). The seasonal species in our study are in essence capital breeders that save reproductive energy during the growing season prior to reproduction.…”