Male alternative reproductive tactics have been observed in two-spotted spider mites Tetranychus urticae, where male-male competition for female access is intense. It has been shown that one's own condition and surrounding environment, such as age and surrounding male density, can affect reproductive tactics. Researchers from the University of Tsukuba, University of Groningen, and University of Vienna reported that the social environment, such as the sex ratio experienced by mothers, can also affect the reproductive behavior of their sons.

Tsukuba, Japan—In the intense male-male competition for females, males often develop alternative reproductive tactics to achieve successful reproduction through unconventional means. These tactics often arise from their own condition and surroundings. However, if mothers can predict the situations their sons will encounter based on their own condition and the surrounding environment, maternal effects are likely to play a significant role in their sons' reproductive tactics.

In this study, researchers focused on the social environment, such as the sex ratio, as a predictor of the intensity of male-male competition. The researchers discovered that in the case of two-spotted spider mites when the sex ratio of the maternal generation is biased toward females, their sons display sneaking tactics and often show early pre-mating guarding. When confronted with a female-biased sex ratio, mothers produce more sons than usual, resulting in more males in the next generation and increased intensity of male-male competition. The male mites mount on the back of the females in the stage just before adulthood as a pre-mating guard. There are two types of males: "fighters," who guard females by fighting, and "sneakers," who do not behave as males and secure a position advantageous for mating without fighting. However, sneakers cannot take over females that are already guarded. Therefore, in situations with more rival males, sneakers will begin pre-mating guarding at an earlier stage. This behavior can be attributed to mothers predicting male-male competition in their son's generation based on the sex ratio of their environment and manipulating their son's reproductive behavior to ensure their reproductive success.

The findings of this study suggest the importance of maternal effects in alternative reproductive tactics in males.

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This study was financially supported by the Japan Society for the Promotion of Science (JSPS) (invitation fellowship L18534 to PS and YS, and KAKENHI grants 17K07556 and 20K06810 to YS).

Original Paper

Title of original paper:

The operational sex ratio experienced by mothers modulates the expression of sons' alternative reproductive tactics in spider mites

Journal:

Behavioral Ecology and Sociobiology

DOI:

10.1007/s00265-023-03370-2

Correspondence

Assistant Professor SATO Yukie
Institute of Life and Environmental Sciences, University of Tsukuba

Related Link

Institute of Life and Environmental Sciences