Effects of global warming on sex ratios in fishes

Abstract

In fishes, sex is determined by genetics, the environment or an interaction of both. Temperature is among the most important environmental factors that can affect sex determination. As a consequence, changes in temperature at critical developmental stages can induce biases in primary sex ratios in some species. However, early sex ratios can also be biased by sex‐specific tolerances to environmental stresses that may, in some cases, be amplified by changes in water temperature. Sex‐specific reactions to environmental stress have been observed at early larval stages before gonad formation starts. It is therefore necessary to distinguish between temperature effects on sex determination, generally acting through the stress axis or epigenetic mechanisms, and temperature effects on sex‐specific mortality. Both are likely to affect sex ratios and hence population dynamics. Moreover, in cases where temperature effects on sex determination lead to genotype–phenotype mismatches, long‐term effects on population dynamics are possible, for example temperature‐induced masculinization potentially leading to the loss of Y chromosomes or feminization to male‐biased operational sex ratios in future generations. To date, most studies under controlled conditions conclude that if temperature affects sex ratios, elevated temperatures mostly lead to a male bias. The few studies that have been performed on wild populations seem to confirm this general trend. Recent findings suggest that transgenerational plasticity could mitigate the effects of warming on sex ratios in some populations.

From gametogenesis to spawning: How climate‐driven warming affects teleost reproductive biology

“…Among the reproductive processes influenced by temperature [ e.g ., sex determination (reviewed by Geffroy & Wedekind, 2020), early puberty], gametogenesis is particularly interesting as during this process gametes are produced and the final stages of oocyte maturation seem to be highly temperature sensitive (Bobe, 2015; Tveiten et al ., 2001; Zucchetta et al ., 2012). Gamete quality is a primary determinate of developmental success in the next generation due to the combined ability of sperm and egg to produce viable offspring (Bobe & Labbé, 2010).…”

Changing climate associated with the range‐wide decline of an estuarine finfish

“…Most of the windows have closed dramatically, by greater than 30 days over the time series, including a 67‐day reduction in the window in only 12 years for Pamlico Sound, NC. Concerns for southern flounder masculinization will only continue to grow with climate change, as warmer temperatures are a threat to natural populations if the skewed sex ratios reduce female reproductive capacity (Geffroy & Wedekind, 2020). These examples of closing development windows further expand the possibility that southern flounder masculinization is occurring range‐wide and could be leading to both declining populations and an increase in cryptic individuals.…”

Low temperature has opposite effects on sex determination in a marine fish at the larval/postlarval and juvenile stages

“…The effect of climate change on species with TSD has long been and remains a subject of great concern (Geffroy & Wedekind, 2020; Janzen, 1994; Mitchell & Janzen, 2010; Ospina‐Alvarez & Piferrer, 2008; Valenzuela et al., 2019), highlighting potential extinction risks, especially in turtles (Jensen et al., 2018; Refsnider & Janzen, 2016; Tomillo et al., 2015). This effect largely depends on the range, but also on the timing of temperature change, that is, on the thermosensitive period.…”