# Fertility and Viability of Hybrid Offspring Imply the Absence of Major Postzygotic Isolation Between Two Reticulitermes Termite Species

## TL;DR

This study shows that hybrid offspring of two termite species are fertile and viable, suggesting weak postzygotic barriers and potential for hybrid population formation.

## Contribution

The study reveals incomplete prezygotic isolation and absence of major postzygotic barriers between two Reticulitermes termite species.

## Key findings

- Hybrid termite colonies produced more eggs and larvae than conspecific colonies.
- Hybrid offspring showed normal body weight, locomotor ability, sex ratio, caste differentiation, and fertility.

## Abstract

Reproductive isolation is essential for maintaining species integrity by limiting interspecific hybridization. In termites, some closely related species can bypass prezygotic isolation and produce hybrids, yet postzygotic barriers remain poorly understood. This study compared reproductive output, body weight, locomotor ability, and hybrid fertility between the hybrid colonies of Reticulitermes flaviceps and R. chinensis and their conspecific colonies. The hybrid colonies displayed higher egg and larval production, with no reduction in body weight or locomotor capacity. The hybrid offspring showed normal sex ratio, caste differentiation, and fertility. These findings indicate an incomplete prezygotic reproductive isolation between the two termites and a potential hybrid population formation. This work supports termite risk management and enriches the understanding of reproductive isolation and speciation in social insects.

(1) Reproductive isolation serves as a critical mechanism that prevents interspecific hybridization among closely related species, thereby preserving species integrity. In termites, hybridization between certain closely related species can overcome prezygotic isolation and produce offspring. However, whether these hybrids can overcome postzygotic barriers remains substantially underexplored. (2) This investigation conducted a comparative analysis of reproductive output (egg production and offspring count), physiological traits (body weight), functional characteristics (locomotor capacity), and hybrid fertility between the hybrid colony that was established by Reticulitermes flaviceps and R. chinensis and the conspecific pairing colonies of R. flaviceps and R. chinensis, respectively. (3) The results showed that hybrid colonies laid significantly more eggs and produced significantly more larvae than conspecific colonies. The hybrid offspring showed no decline in weight and locomotor capacity. Furthermore, the hybrid offspring maintained balanced sex ratios with unimpaired caste differentiation and fertility in both sexes. (4) These results demonstrate that the prezygotic reproductive isolation mechanism is incomplete between two closely related termite species, and there is a risk of forming hybrid populations. This work not only provides a theoretical basis for monitoring the risk of hybrid populations in termite management but also offers new insights into the evolution of reproductive isolation and speciation in social insects.