Constant diurnal temperature regime alters the impact of simulated climate warming on a tropical pseudoscorpion

Abstract

Recent theory suggests that global warming may be catastrophic for tropical ectotherms. Although most studies addressing temperature effects in ectotherms utilize constant temperatures, Jensen's inequality and thermal stress considerations predict that this approach will underestimate warming effects on species experiencing daily temperature fluctuations in nature. Here, we tested this prediction in a neotropical pseudoscorpion. Nymphs were reared in control and high-temperature treatments under a constant daily temperature regime, and results compared to a companion fluctuating-temperature study. At constant temperature, pseudoscorpions outperformed their fluctuating-temperature counterparts. Individuals were larger, developed faster, and males produced more sperm, and females more embryos. The greatest impact of temperature regime involved short-term, adult exposure, with constant temperature mitigating high-temperature effects on reproductive traits. Our findings demonstrate the importance of realistic temperature regimes in climate warming studies, and suggest that exploitation of microhabitats that dampen temperature oscillations may be critical in avoiding extinction as tropical climates warm.

Figure 1. Male and female reproductive traits in Cordylochernes scorpioides.

(a) A sperm packet (stained red) with everted tube and evacuated sperm (stained green). (b) Ventral view of a female carrying a brood sac of approximately 100 early-stage embryos. The images are reproduced from Ref. .

Figure 2. Size and level of sexual dimorphism decline significantly in response to high temperature.

Shown are means (±SE) of chela hand depth in males (triangles) and females (circles) under control and high temperature conditions. The image at the lower left indicates the measured trait, chela hand depth. Images of average-sized males from the control and high temperature treatments are shown at the upper left and lower right of the figure, respectively.

Figure 3. Proportion of females becoming gravid depends on both female and male temperature treatment.

Shown are the mean proportion of females producing a brood sac of early-stage embryos as a function of the female's temperature treatment and the temperature treatment of her mate.

Figure 4. Temperature treatment experienced by females and their mates significantly affects embryo production.

The mean (±SE) number of early-stage embryos is shown for the four experimental treatments. C and H (control and high temperature, respectively) indicate temperature treatment experienced by an individual throughout development and adulthood.

Figure 5. Constant temperature regime decreases development time of males and females at both control and high temperatures.

The mean (±SE) development time in days from birth to adult is shown for each of the eight experimental treatments.

Figure 6. Constant temperature regime increases sperm number in all regime x temperature combinations.

The mean (±SE) number of sperm per sperm packet is shown for each of the eight experimental treatments.

Figure 7. Constant temperature regime increases sperm viability in all regime x temperature combinations.

The mean (±SE) proportion of live sperm per sperm packet is shown for each of the eight experimental treatments.

Figure 8. Constant temperature regime increases number of embryos produced by females in all regime x temperature combinations.

The mean (±SE) number of embryos per brood sac is shown for each of the eight experimental treatments.