Journal
FRESHWATER BIOLOGY
Volume 67, Issue 9, Pages 1644-1655Publisher
WILEY
DOI: 10.1111/fwb.13969
Keywords
crowding; ephippia production; gene JHAMT; sex ratio; structural equation model
Categories
Funding
- National Natural Science Foundation of China [31730105]
- Priority Academic Program Development of Jiangsu Higher Education Institutions
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Predation risk and crowding can induce sexual reproduction in Daphnia. This study investigated whether sexual reproduction is caused directly by fish kairomones or indirectly through kairomone-induced crowding. The results showed that population density, rather than fish kairomone, was the significant factor promoting sexual reproduction in Daphnia populations.
Both predation risk and crowding can induce sexual reproduction in Daphnia, and predator kairomones can also cause population crowding. It is, however, unclear as to whether sexual reproduction is caused by kairomone per se or indirectly by kairomone-induced crowding. In this study, we cultured Daphnia pulex in the presence of fish kairomone, with newborn offspring being retained (increasing population density) or removed (constant population density). The relationships among fish kairomone, population density, and indicators of sexual reproduction were assessed using structural equation models. The results showed that when offspring were retained in the population, the population density and sexual reproduction by Daphnia simultaneously increased in response to the presence of the fish kairomone, whereas sexual reproduction was not directly affected in the presence of fish kairomones alone. Conversely, when maintaining a constant population density, the number of ephippia and ratio of male to female of Daphnia increased with increasing population density, but the presence of fish kairomone did not promote sexual reproduction. Structural equation model analysis indicated that population density, rather than the fish kairomone, was the significant factor promoting sexual reproduction. The findings of this study indicate that population density directly triggers sexual reproduction in Daphnia populations. Our observations provide new insights into environmentally induced sexual reproduction, and on this basis, we suggest that a more thorough consideration of the interactions among environmental factors in determining sexual reproduction is necessary.
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