Warm waters undermine cryptic female choice

(1)  Understanding the thermal sensitivity of reproductive
interactions is crucial given global warming. Previous studies have almost
exclusively focused on interactions before mating, even though important
interactions between the sexes also occur after mating (e.g., gamete
interactions), which are likely affected by temperature. (2) 
Thus, it remains unknown how temperature affects the influence of female
reproductive fluid on sperm performance, thereby altering female control
over fertilization (cryptic female choice). This gap limits our
understanding of how sexual selection changes with seasonal temperature
fluctuations and temperatures outside the range of historical norms.
(3)  We tested how temperatures relevant to current conditions
and climate change projections influence the mechanisms underlying cryptic
female choice in a marine fish, Symphodus ocellatus. Under typical thermal
conditions, female reproductive fluid enhances sperm velocity and biases
fertilization dynamics to favor preferred, dominant males over sneaker
males. (4)  We find that warmer temperatures decrease female
influence on sperm velocity, especially for dominant males. This results
in dominant males having slower sperm than sneaker males at warmer
temperatures, reducing the expected paternity of preferred, dominant
males. (5)  Our results highlight that considering the thermal
sensitivity of female-male interactions that occur after mating will be
essential for understanding how seasonal variation and climate change can
influence fertility, reproduction, and sexual selection.