Greater reproductive investment, but shorter lifespan, in agrosystem than in natural-habitat toads

Abstract

Global amphibian decline is due to several factors: habitat loss, anthropization, pollution, emerging diseases, and global warming. Amphibians, with complex life cycles, are particularly susceptible to habitat alterations, and their survival may be impaired in anthropized habitats. Increased mortality is a well-known consequence of anthropization. Life-history theory predicts higher reproductive investment when mortality is increased. In this work, we compared age, body size, and different indicators of reproductive investment, as well as prey availability, in natterjack toads (Epidalea calamita) from agrosystems and adjacent natural pine groves in Southwestern Spain. Mean age was lower in agrosystems than in pine groves, possibly as a consequence of increased mortality due to agrosystem environmental stressors. Remarkably, agrosystem toads were larger despite being younger, suggesting accelerated growth rate. Although we detected no differences in prey availability between habitats, artificial irrigation could shorten aestivation in agrosystems, thus increasing energy trade. Moreover, agrosystem toads exhibited increased indicators of reproductive investment. In the light of life-history theory, agrosystem toads might compensate for lesser reproductive events—due to shorter lives—with a higher reproductive investment in each attempt. Our results show that agrosystems may alter demography, which may have complex consequences on both individual fitness and population stability.

Early swelling response to phytohemagglutinin is lower in older toads

“…Accordingly, Hyla arborea male frogs showed no negative effect of testosterone injection on swelling response to PHA (Desprat et al, 2015). Indeed, immune responsiveness to PHA has often been found similar in male and female anurans (Zhang et al, 2017), also in this species (Zamora-Camacho & Comas, 2017).…”

“…Conversely, an immune challenge can trigger terminal investment (Bonneaud et al, 2004; Nielsen & Hokman, 2012), suggesting complex relationships between immune system and reproduction in the context of ageing. Indeed, reproduction and immune activity are under a trade-off in great tit ( Parus major ) females (Ots & Horak, 1996), as could also be happening in this system, where some indicators of reproductive investment are higher in older individuals in E. calamita toads (Zamora-Camacho & Comas, 2017).…”

“…Furthermore, we detected no effect of habitat on the negative relationship between age and early immune response. These agrosystem toads live shorter but grow larger and invest more in reproduction (Zamora-Camacho & Comas, 2017), and at the same time they show a delayed early swelling response to PHA in comparison with natural-habitat toads (Zamora-Camacho, in press). Therefore, we might expect accelerated reduction of early immune response in agrosystem toads due to agrosystem stressors.…”

“…Prior to their release, we clipped two toes from each toad, disinfecting the wounds with chlorhexidine and stanching them with a tissue adhesive glue (Dermabond). Toes were used for age estimates, as previously described in Zamora-Camacho & Comas (2017). Specifically, age was estimated by means of phalanx skeletochronology (Comas et al, 2016) using one phalanx per toad.…”

“…In this work, we test the hypothesis that older natterjack toads ( Epidalea calamita ) should elicit an early immune response (corresponding to an innate-response stage; Brown, Shilton & Shine, 2011) less intense than younger conspecifics. Moreover, we compare toads from natural habitats with conspecifics from agrosystems, since the latter show delayed early swelling response to PHA (Zamora-Camacho, in press), most likely due to the physiological stress caused by agrosystem conditions (Zamora-Camacho & Comas, 2017). Plus, we compare males and females, because the pattern of early swelling response to PHA is different between sexes in this species (Zamora-Camacho, in press), probably due to the greater reproductive investment of females through egg production (Tejedo, 1992), and/or the immunosuppresor effect of testosterone in males (Folstad & Karter, 1992).…”