Geographic variation in life‐history traits: factors shaping energy investment in reproduction in a highland dwelling rodent

Abstract

Variation in life‐history traits is shaped by intrinsic and extrinsic factors. Climate influences the availability of energy and nutrients in the environment, and thus animals’ energy balance, their allocation of resources to reproduction and ultimately, fitness. Temperature is reported as a prevailing influence on animals’ investment in reproduction, and diverse hypotheses propose mechanisms by which it occurs. Central and external limits to energy acquisition have been traditionally assumed. Hence, digestive limitations, periods of low food availability or demanding cold conditions would restrict this input. However, under warm conditions endotherms also face the need to dissipate heat from metabolic processes. From this perspective, a high metabolic rate process, such as lactation, would be restricted under increasing ambient temperatures (Ta). Our research addresses the variation in reproductive parameters in Phyllotis xanthopygus, a rodent species broadly distributed in the west highlands and southern parts of South America. Across a pronounced elevation gradient in the central Andes Mountains we found that litter size is comparatively smaller in pregnant females collected at lower elevations. This is congruent with expectations from the heat dissipation limit hypothesis. To disentangle the role of temperature on this pattern, we bred individuals under two thermal treatments. We recorded no changes in the litter size, but pups’ body mass was lower at higher Ta during lactation, also in agreement with decreased metabolism. Offspring size and number are relevant to a species’ fitness. The evidence suggests that in P. xanthopygus these traits vary geographically and are shaped by Ta in the laboratory. A species that evolved in high altitudes, inhabits cold and temperate areas and is sensitive to Ta increases in the laboratory, appears as an excellent candidate to further explore the ecophysiology‐thermal landscape interface, crucial to develop accurate predictive models of biodiversity dynamics.

Heat dissipation rate constrains reproductive investment in a wild bird

“…Szafrańska et al, 2014;Nord & Folkow, 2018). It is interesting to speculate that any such geographical variation in the nature of the limits to sustained energy expenditure may help explain why high-altitude populations of some species produce larger broods than low-latitude populations (Sassi, Menéndez, & Cuevas, 2018), or provide insights into answers for the long-disputed question of why clutch size in birds increases poleward from the equator (Ricklefs, 2000).…”

Evolved changes in maternal care in high-altitude native deer mice

“…In rodents with broad altitudinal distributions, females from populations at higher elevations tend to give birth to larger litters than their low altitude counterparts, likely to compensate for this shorter breeding season (e.g. Phyllotis xanthopygus, Sassi et al, 2018;P. maniculatus, Dunmire, 1960;Halfpenny, 1980;McLean et al, 2019).…”

Phenotypic plasticity in the energy metabolism of a small Andean rodent: Effect of short‐term thermal acclimation and developmental conditions

“…A temperature limitation to energy expenditure becomes particularly relevant if it affects high energy‐demanding processes such as reproduction. In fact, previous work on our study species found that mean pup weight during lactation was higher for dams acclimated at 16°C than at 31°C (Sassi et al, 2018) and that there is a positive correlation between RMR of the dam and litter mass (Sassi et al, 2019). Hence, the relatively high conductance of the F1 could be advantageous under warm conditions as it allows to maintain a higher energy expenditure, but it implies higher thermoregulatory costs at low ambient temperatures.…”

“…Concerning temperature, there is a marked decrease both in mean temperature and in thermal amplitude towards higher elevations. Ambient temperature data characterizing the selected sites was reported by previous studies (Ruperto et al, 2020; Sassi et al, 2015, 2018) and is presented in Table 1.…”