Mating systems and reproductive ecology


sexual selection, monogamy, promiscuity, multiple mating, extra-pair paternity, mate choice, reproductive success, secondary sexual characters, fighter and sneaker mating tactics, inter-specific hybridization

Study species

Dolly Varden, white-spotted charr, invasive brook trout, masu salmon, brook lamprey, Japanese daces, Japanese tits, other passerine birds

Everyone likes mating ecology! Reproduction is the most important event during an animal’s life. Not only is it an attractive topic, but reproduction also provides us good with data since many otherwise difficult to find animals gather in specific breeding areas. Many students and pos-docs study reproductive ecology and we’ll introduce three of their topics here.

“Who is your daddy?”

For their monogamous nature, birds are often symbols of good couples. In early 1990’s, however, this conventional view had been completely overturned. Genetic parentage analyses have revealed more than 90% of socially monogamous birds produce extra-pair offspring. This invoked numerous studies on patterns, causes, and consequences of extra-pair mating in many bird species. Interesting and fascinating hypotheses have been proposed so far. However, due to the difficulty in field surveys, most hypotheses have not been fully examined. We experimentally manipulate breeding pairs of Japanese tits to solve some of these problems. We’ll describe more details when published!


Is that cooperation?

Cooperation or collaboration is common in humans (actually, necessary). However, this is very rare in wild animals except for some social mammals and birds. In terms of fitness, helping other individuals is generally unfavorable: altruistic behavior will not evolve in non-social animals. Brook lamprey exhibit an apparent cooperative behavior, which is unexpected for non-social, promiscuous organisms. They dig nests on stream beds by removing gravel. Males rarely attack each other, rather they remove gravels together (interestingly, females also do). It would seem that cheaters (i.e. those that don’t remove stones but concentrate on mating) are the greatest advantage, however interestingly we don’t see such behavior in males. To examine if males that remove more stones have higher mating success and if females can choose specific partners from a large number of surrounding males, we identified individuals with fluorescent elastomer tags and recorded mating behavior in great detail.



How many babies do you have?

It is natural for ecologists to want to assess how much offspring each individual produces or what their survival rate is in the wild. Recent advances in molecular techniques and individual’s tracking systems make them possible. In the Sorachi River, introduced brook trout hybridize with native white-spotted charr. To investigate the future trends we are investigating survival and reproductive success of the native, introduced, and hybrid fishes. We are particularly interested in strong secondary sexual characteristics of brook trout. Elongated kype (nose), deep bodies, and bright colorations are believed to be advantageous for sexual selection. Hybrids should exhibit intermediate characteristics and reproductive success might be lower than parental species. We collected as many candidate parents and offspring as possible. We are just getting interesting results!