Water turbidity constrains male mating success in a marine fish

Abstract

Human-induced eutrophication, resulting in increased algal growth and water turbidity, is an alarming problem in aquatic systems. Many studies have focused on the effects of algal turbidity on mate choice and sexual selection in fish, but little emphasis has been given to the ways it can constrain mating success. Here we experimentally investigated the effects of algal turbidity on maximum male mating success and parental care in the sand goby, Pomatoschistus minutus, a fish with a resourcedefence mating system and male parental care. For this purpose, we introduced to 1 nest-holding male 5 random-sized ripe females in either clear or in turbid water. After spawning, we observed how many mates and eggs the male received and followed his parental behaviour and egg survival for 6 days under turbid or clear water conditions. When spawning took place in clear water, the number of eggs the male received into his nest increased with the total weight of five females in his tank. However, when spawning took place in turbid water, there was no relationship between female size and the number of eggs laid, although the number of females that spawned was the same as in clear water. The results indicate that females adjust the number of eggs they lay according to water turbidity. This could explain previous findings that mating success is more evenly distributed among males in turbid than clear water conditions. Significance statementThe first responses of animals to human-induced changes in the environment are behavioural. Subtle changes in the behaviour of individuals can have profound consequences for populations and communities. Human-induced eutrophication, leading to algal blooms and water turbidity, is a major environmental problem in aquatic systems worldwide. Our results on the sand goby suggest a new mechanism by which water turbidity may affect fish mating systems and weaken sexual selection. When spawning takes place in clear water, the number of eggs accumulated in a males' nest is an increasing function of the fecundity of the females. However, when spawning in turbid water, this positive relationship between female size and egg numbers disappears. We believe this is because females do not perceive the competition from other females in turbid water and therefore invest less in present reproduction.

Editorial: Sexual selection and environmental change: what do we know and what comes next?

“…For example, increased turbidity following algal blooms causes three-spined stickleback, Gasterosteus aculeatus , males to invest more time and energy courting females but with no corresponding increase in successful female attraction ( Candolin et al 2007 ). In the sand goby Pomatoschistus minutus , increased turbidity alters females’ perception of intra-sexual competition, resulting in reduced male reproductive success ( Järvenpää et al 2019 ). In insects, changes in temperature are known to affect odor profiles, which can influence female mate choice, as observed in the red mason bee Osmia bicornis ( Conrad et al 2017 ).…”

Insights into adaptive behavioural plasticity from the guppy model system

“…Water turbidity, the level of light scattered in a liquid, has been steadily increasing in freshwater habitats worldwide due to anthropogenic impacts. Decreases in light availability reduce the visual cues and communication available and impact a variety of behaviours in fish such as shoaling [69], anti-predator responses [70], foraging [71] and mating behaviour [72]. Guppies are exposed to natural fluctuations in turbidity daily, weekly and seasonally, but as Trinidad is increasingly impacted by rock quarries and deforestation, guppies are being exposed to longer and more intense bursts and higher baseline levels of turbidity in some streams [73,74].…”

The influence of water turbidity on the spawning success of giant gourami Osphronemus goramy Lacepède, 1801

“…Furthermore, it is reported that the turbidity value greatly affects the life of aquatic biota [6], [12], so it is likely to affect significantly the proportion of spawning broodstock and the degree of fertilization rate of gourami because spawning occurs naturally [13]. [11] suggested that water turbidity affects the success of fish spawning.…”

“…However, [11] also reported that fish spawning would be more prevalent in turbid waters than in clear waters. It can be understood that in waters that are too clear, fish will be disturbed by the noise around the pond; therefore, it is a consideration in determining the layout of spawning ponds away from the crowd, or there is an effort to prohibit activities around the pond, especially during certain hours for spawning.…”

“…Furthermore, it was found that spawning in clear water increased fecundity. According to the research by [11], male fish experienced reduced attention from females or even avoidance of spawning in turbid water. This behavior could be attributed to male fish's challenges in protecting many eggs, leading them to cease their courtship behaviors.…”