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Male coercive mating in externally fertilizing species: male coercion, female reluctance and explanation for female acceptance.

Matsumoto Y, Takegaki T - Sci Rep (2016)

Bottom Line: Most males that used small, tight nests acquired new eggs but with experimentally enlarged nests, 90% of the males without eggs failed to confine the females.In the nests where the first eggs were deposited in the early period, subsequent matings with other females were more likely to occur, whereas in the late period, most parental care of the eggs failed without additional matings.The females that spawned in the late period may have been compelled to accept male coercive mating due to time constraints.

View Article: PubMed Central - PubMed

Affiliation: Center for Coastal Fisheries and Aquaculture, Tohoku National Fisheries Research Institute, Fisheries Research Agency, Iwate, Japan.

ABSTRACT
Male coercive mating exerts a strong evolutionary pressure on mating-related traits of both sexes. However, it is extremely rare in externally fertilizing species probably because the male mating behaviour is incomplete until females release their eggs. Here we showed that males of the externally fertilizing fish Rhabdoblennius nitidus coercively confine females to the nests until spawning, and investigated why females accept male coercive mating. The females entered the males' nests following male courtship displays, but they usually tried to escape when there were no eggs because males tended to cannibalize all the eggs when there were few. Most males that used small, tight nests acquired new eggs but with experimentally enlarged nests, 90% of the males without eggs failed to confine the females. Spawning tended to occur during the early/late spawning period in nests with no eggs (i.e. male coercive mating). In the nests where the first eggs were deposited in the early period, subsequent matings with other females were more likely to occur, whereas in the late period, most parental care of the eggs failed without additional matings. The females that spawned in the late period may have been compelled to accept male coercive mating due to time constraints.

No MeSH data available.


Related in: MedlinePlus

(a) Nesting male (left) pushing a female back into the nest (small double-layered nest) from the outside. (b,c) Nesting male plugging the nest by bending its body in the nest. Image (c) shows a view from behind the nest where the bottom plug was removed temporarily for the photograph. (d) Female passing through the gap between the male’s body and the inside wall of the enlarged nest. Comparison between the proportion of males that spawned with females when they had eggs and when they did not have eggs in the small nest (e) and enlarged nest (f).
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f1: (a) Nesting male (left) pushing a female back into the nest (small double-layered nest) from the outside. (b,c) Nesting male plugging the nest by bending its body in the nest. Image (c) shows a view from behind the nest where the bottom plug was removed temporarily for the photograph. (d) Female passing through the gap between the male’s body and the inside wall of the enlarged nest. Comparison between the proportion of males that spawned with females when they had eggs and when they did not have eggs in the small nest (e) and enlarged nest (f).

Mentions: Rhabdoblennius nitidus (Blennidae) is a marine fish with external fertilization, which inhabits rocky intertidal shores. The males occupy small rock holes or vacant gastropod shells as spawning nests, and they accept eggs from several females17. The eggs are attached inside the nests and tended by the male alone until hatching (ca. 7 days)17. The male reproductive activity varies between courtship and parental phases according to androgen-mediated brood cycling18. After the male has acquired eggs from the first female, it exhibits courtship displays for only the next 2 days because of the shift from courtship to the parental phase18. If the male acquires few eggs during the courtship phase, all of the eggs are usually eaten by the male, probably due to the expected low reproductive return from the parental care investment19. Therefore, females prefer males with more eggs in their nests20. Male coercive-like mating often occurs when a female enters an eggless nest following male courtship displays. The nesting male seems to push the female deeper into the nest (Fig. 1a) and to plug the nest by bending its body (Fig. 1b,c). However, it is difficult to demonstrate whether these male behaviours are coercive mating because they appear to be part of the spawning behaviour, such as sperm release behaviour. A simple way to provide evidence of male coercive mating is to disable male traits that are specialized for coercive mating, as demonstrated in some insects2122 but such specific morphological traits are not observed in R. nitidus males. In some substrate brooding fishes including R. nitidus, nesting males show the strong preference for a size-matched tight nest232425 probably due to the advantage for guarding against egg predators23. We focused on the male size-assortative nest preference and hypothesized that a narrow gap between the male’s body and the nest’s inner wall may also be beneficial to the male if the gap allows it to confine females in the nest. Therefore, the first aim of this study was to experimentally demonstrate that R. nitidus males coercively confine reluctant females in the nests until spawning has occurred.


Male coercive mating in externally fertilizing species: male coercion, female reluctance and explanation for female acceptance.

Matsumoto Y, Takegaki T - Sci Rep (2016)

(a) Nesting male (left) pushing a female back into the nest (small double-layered nest) from the outside. (b,c) Nesting male plugging the nest by bending its body in the nest. Image (c) shows a view from behind the nest where the bottom plug was removed temporarily for the photograph. (d) Female passing through the gap between the male’s body and the inside wall of the enlarged nest. Comparison between the proportion of males that spawned with females when they had eggs and when they did not have eggs in the small nest (e) and enlarged nest (f).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834473&req=5

f1: (a) Nesting male (left) pushing a female back into the nest (small double-layered nest) from the outside. (b,c) Nesting male plugging the nest by bending its body in the nest. Image (c) shows a view from behind the nest where the bottom plug was removed temporarily for the photograph. (d) Female passing through the gap between the male’s body and the inside wall of the enlarged nest. Comparison between the proportion of males that spawned with females when they had eggs and when they did not have eggs in the small nest (e) and enlarged nest (f).
Mentions: Rhabdoblennius nitidus (Blennidae) is a marine fish with external fertilization, which inhabits rocky intertidal shores. The males occupy small rock holes or vacant gastropod shells as spawning nests, and they accept eggs from several females17. The eggs are attached inside the nests and tended by the male alone until hatching (ca. 7 days)17. The male reproductive activity varies between courtship and parental phases according to androgen-mediated brood cycling18. After the male has acquired eggs from the first female, it exhibits courtship displays for only the next 2 days because of the shift from courtship to the parental phase18. If the male acquires few eggs during the courtship phase, all of the eggs are usually eaten by the male, probably due to the expected low reproductive return from the parental care investment19. Therefore, females prefer males with more eggs in their nests20. Male coercive-like mating often occurs when a female enters an eggless nest following male courtship displays. The nesting male seems to push the female deeper into the nest (Fig. 1a) and to plug the nest by bending its body (Fig. 1b,c). However, it is difficult to demonstrate whether these male behaviours are coercive mating because they appear to be part of the spawning behaviour, such as sperm release behaviour. A simple way to provide evidence of male coercive mating is to disable male traits that are specialized for coercive mating, as demonstrated in some insects2122 but such specific morphological traits are not observed in R. nitidus males. In some substrate brooding fishes including R. nitidus, nesting males show the strong preference for a size-matched tight nest232425 probably due to the advantage for guarding against egg predators23. We focused on the male size-assortative nest preference and hypothesized that a narrow gap between the male’s body and the nest’s inner wall may also be beneficial to the male if the gap allows it to confine females in the nest. Therefore, the first aim of this study was to experimentally demonstrate that R. nitidus males coercively confine reluctant females in the nests until spawning has occurred.

Bottom Line: Most males that used small, tight nests acquired new eggs but with experimentally enlarged nests, 90% of the males without eggs failed to confine the females.In the nests where the first eggs were deposited in the early period, subsequent matings with other females were more likely to occur, whereas in the late period, most parental care of the eggs failed without additional matings.The females that spawned in the late period may have been compelled to accept male coercive mating due to time constraints.

View Article: PubMed Central - PubMed

Affiliation: Center for Coastal Fisheries and Aquaculture, Tohoku National Fisheries Research Institute, Fisheries Research Agency, Iwate, Japan.

ABSTRACT
Male coercive mating exerts a strong evolutionary pressure on mating-related traits of both sexes. However, it is extremely rare in externally fertilizing species probably because the male mating behaviour is incomplete until females release their eggs. Here we showed that males of the externally fertilizing fish Rhabdoblennius nitidus coercively confine females to the nests until spawning, and investigated why females accept male coercive mating. The females entered the males' nests following male courtship displays, but they usually tried to escape when there were no eggs because males tended to cannibalize all the eggs when there were few. Most males that used small, tight nests acquired new eggs but with experimentally enlarged nests, 90% of the males without eggs failed to confine the females. Spawning tended to occur during the early/late spawning period in nests with no eggs (i.e. male coercive mating). In the nests where the first eggs were deposited in the early period, subsequent matings with other females were more likely to occur, whereas in the late period, most parental care of the eggs failed without additional matings. The females that spawned in the late period may have been compelled to accept male coercive mating due to time constraints.

No MeSH data available.


Related in: MedlinePlus