Female fish judge males based on their ability to design nests best suited for the conditions of their environment, according to a new study by University of Leicester researchers.
In the study, biologists at the University of Leicester, the Australian National University (ANU) and the University of Technology Sydney (UTS) have shown that low oxygen can change the way in which fish build nests, and also change the nesting preferences of female fish.
Male three-spined stickleback fish are unusual in that they build nests and provide all the parental care for the eggs, which are spawned by females, and for the developing baby fish.
The research team found that males change the design of their nests depending on the oxygen content of the water – making looser nests under low-oxygen conditions and more compact nests when oxygen increases.
Fish are under threat from a wide range of man-made environmental changes, including global warming and pollution, and together these can lead to reduced oxygen levels in aquatic habitats.
In the worst cases this can lead to large-scale fish kills, but low oxygen can also affect critically important reproductive behaviours, with associated effects on the viability of fish populations and even implications for natural selection and evolution.
The research has shown that it was not just male construction that was affected when water oxygen levels changed.
The most interesting finding was that female fish also changed their preferences for the design of nest they went for.
Female choices flipped from preferring tighter nests under high oxygen condition, to preferring looser nests when conditions deteriorated.
What is really cool about this result is that females seem to have flexible preferences for the type of nest they preferred.
They did not always choose a particular nest design, but they chose the nest that was best designed for the particular conditions they were experiencing at the time.
Interestingly, this flexibility was limited to their nest preferences: females always chose the biggest, most vigorously courting males irrespective of the oxygen level.
These flexible nest preferences might give sticklebacks a real advantage in rapidly changing environments.
One problem animals in degraded habitats often face is that the decisions they make are shaped by their evolutionary history, with the result that they end up making choices that are no longer beneficial under changed conditions.
The fact that sticklebacks appear to be able to moderate their behaviour and their decision-making dependent on local conditions might mean they might be able to cope better in degraded environments.
Citation: Head ML, et al. (2016) Environmental change mediates mate choice for an extended phenotype, but not for mate quality. Evolution, published online. DOI: 10.1111/evo.13091.
Figure legend: This Knowridge.com image is credited to Sergey Yeliseev.