Caste development and sex ratio of the Ryukyu drywood termite Neotermes sugioi and its potential mechanisms

Y Miyaguni,A Agarie,K Tsuji,K Kobayashi,K Sugio

doi:10.1038/s41598-021-94505-w

Y Miyaguni, A Agarie + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-94505-w

Copy DOI

Abstract

Sex allocation is one of the most studied traits in evolutionary biology because its theoretical predictions match the empirical data. Here, using the Ryukyu dry-wood termite Neotermes sugioi, we investigated several factors that could bias the sex allocation in three populations (Okinawa, Ishigaki/Iriomote, and Yonaguni). Our survey showed that there were more queen-only colonies than king-only colonies in these populations, suggesting a longer lifespan of the queens than that of the kings. In this condition, sex-asymmetric reproductive value (SRV) theory predicts female bias, because even after the short-lived kings die, the long-lived queens can continue reproduction with their sons. However, sex allocation in this species seemed to be biased toward males. Furthermore, we examined the possibility of intrasexual competition among siblings (ICS). If ICS is the cause of the bias, the allocation is expected to change depending on the total investment in sexual offspring. However, the biomass of both male and female alates increased linearly with the increase in the total biomass of the alates in these populations. Thus, neither the SRV nor the ICS theory could explain the male-biased sex ratio of N. sugioi. On the basis of these results, we discuss the remaining possibilities in this species.

Highlights

Sex allocation is one of the best-studied cases of adaptation, as theoretically predicted optima match well with the observed values
If biased sex allocation is caused by intrasexual competition among siblings (ICS), it would be expected that allocation change depending on the available resources for the colony, which results in a strategy of constant investment into the rare sex[2,9,10]
The frequency of reproductives in the field colonies suggested that the queens live longer than the kings, and the sex-asymmetric reproductive value (SRV) theory, which predicts female bias, cannot explain the observed male-biased sex ratio in alates (Fig. 2c)

Summary

Introduction

Sex allocation is one of the best-studied cases of adaptation, as theoretically predicted optima match well with the observed values. The primary queen will mate with the secondary neotenic king (her son), whereas on the other hand, due to the presumable obligate pre-copulatory dispersal in female alates, the primary king does not have an opportunity to mate with the secondary queen (his daughter) and dies without reproduction after the death of his partner In this condition, the SRV theory predicts female-biased sex a llocation[5]. The strong selective pressure of ICS can bias sex allocation toward males despite SRV In this case, it is expected that the biomass of male alates remains constant even if the total alate biomass produced by the colony is large while production of female alates increases linearly with the total alate biomass[2,9]. We discussed the remaining possibilities to explain this inconsistency

Methods

Results

Conclusion