Degrees of disruption: projected temperature increase has catastrophic consequences for reproduction in a tropical ectotherm

Abstract

Although climate change models predict relatively modest increases in temperature in the tropics by the end of the century, recent analyses identify tropical ectotherms as the organisms most at risk from climate warming. Because metabolic rate in ectotherms increases exponentially with temperature, even a small rise in temperature poses a physiological threat to tropical ectotherms inhabiting an already hot environment. If correct, the metabolic theory of climate warming has profound implications for global biodiversity, since tropical insects and arachnids constitute the vast majority of animal species. Predicting how climate change will translate into fitness consequences for tropical arthropods requires an understanding of the effects of temperature increase on the entire life history of the species. Here, in a comprehensive case study of the fitness consequences of the projected temperature increase for the tropics, we conducted a split-brood experiment on the neotropical pseudoscorpion, Cordylochernes scorpioides, in which 792 offspring from 33 females were randomly assigned at birth to control-and high-temperature treatments for rearing through the adult stage. The diurnally varying, control treatment temperature was determined from long-term, average daily temperature minima and maxima in the pseudoscorpion's native habitat. In the high temperature treatment, increasing temperature by the 3.5°C predicted for the tropics significantly reduced survival and accelerated development at the cost of reduced adult size and a dramatic decrease in level of sexual dimorphism. The most striking effects, however, involved reproductive traits. Reared at high temperature, males produced 45% as many sperm as control males, and females failed to reproduce. Sequencing of the mitochondrial ND2 gene revealed two highly divergent haplogroups that differed substantially in developmental rate and survivorship but not in reproductive response to high temperature. Our findings suggest that reproduction may be the Achilles' heel of tropical ectotherms, as climate warming subjects them to an increasingly adverse thermal environment.

The effects of elevated temperature on the sexual traits, immunology and survivorship of a tropical ectotherm

“…Zeh et al, 2012) (reviewed in Pepin, 1991). Although temperature can impact many aspects of natural ecosystems (reviewed in Ficke et al, 2007;IPCC, 2007), establishing its direct effect on physiology and survival is a crucial first step in discerning the impact of climate change on natural populations.…”

“…Williot et al, 2000), decreased sperm number (e.g. Zeh et al, 2012) and, in one study, increased sperm length (e.g. Blanckenhorn and Hellriegel, 2002); most other stressors have, in contrast, been shown to lead to decreased sperm length (e.g.…”

Sisters' curse: sexually antagonistic effects constrain the spread of a mitochondrial haplogroup superior in sperm competition

“…Female fecundity and reproductive success were assessed based on the number of early stage embryos produced and the number of protonymphs born to each female, respectively. Matings were carried out, as described elsewhere [27], and females were then monitored until they either gave birth to protonymphs, spontaneously aborted their brood of embryos or failed to become gravid within 30 days. Gravid females were carefully removed from their vials as soon as individual embryos became clearly discernable, and digital images of their brood sacs were recorded for embryo counting, as described elsewhere [41].…”

“…External spermatophore deposition and diagnostic female behaviour facilitate unambiguous assessment of female sexual receptivity and success of sperm transfer. Non-invasive monitoring of female reproductive status and embryological development is made possible by C. scorpioides' 'external womb' mode of viviparity, in which females nourish developing embryos in an external, transparent brood sac overlying their genital aperture [27]. In the wild, C. scorpioides females produce mixed-paternity broods sired by up to four males [30], and sperm competitive ability is therefore likely to be an important component of male fitness in this pseudoscorpion.…”

Responses of Insect Pests and Plant Diseases to Changing and Variable Climate: A Review

“…There is, therefore, a risk that future crop yields might be overestimated if the impacts of insect pests and plant disease epidemics are not taken into consideration (West et al, 2015). In the tropical areas, there have been few studies on the effect of global warming on insect pests of agricultural crops (Perkins et al, 2011) with the exception of the coffee berry borer (Jaramillo et al, 2009) and the potato tuber moth (Kroschel et al, 2013) and yet tropical insects are at a greater risk from climate change as they inhabit hot environments (Zeh et al, 2012). This review will, therefore, examine the impact of each of the climate change variable in more detail.…”