Fig. 2 Castes and subcastes of the white-footed ant Technomyrmex brunneus. 1: dealate queen. 2, 3: major intercaste (2: head, 3: alitrunk and petiole). 4, 5: medium intercaste (4: head, 5: alitrunk and petiole). 6, 7: minor intercaste (6: head, 7: alitrunk and petiole). 8–10: worker (8: head, 9: alitrunk, petiole and gaster, 10: propodeum and petiole, dorsal view). 11: winged male, head. 12: wingless male, head. This figure is a reprint from Terayama et al. (2021a) under permission from the Myrmecological Society of Japan. E. SUNAMURA et al. from spring in autumn, to summer and decreases suggesting that reproductive activity is highest from late spring to summer (Kobayashi et al., 2024a). 4.2 Unicoloniality Technomyrmex brunneus is polydomous. Colony sizes vary among locations, and multiple, mutually exclusive colonies coexist on Okinawa and the Ogasawara Islands (Putri et al., 2021). The size of each colony is still large, however, with approximately 420,000 individuals on average and 2,900,000 individuals in the largest (Yamauchi et al., 1991). For example, Yamauchi et al. (1991) observed that a colony fragment included at least 15 nests which were connected by ant trails and spanned over 30 m. On Hachijo Island, none of the T. brunneus nests collected from various locations across the distribution area were hostile to each other, suggesting that they formed a single supercolony across the 62.52 km2 island (Ogura et al., 2017; Putri et al., 2021). A supercolony is defined as the entity of numerous physically separated nests extending over a long range (more than several hundred meters), across which individuals can move freely without facing territorial aggression. In Kagoshima Prefecture, five populations sampled over 50 km were mutually non-aggressive or weakly aggressive, suggesting that an area-wide supercolony was being constructed there (Kobayashi et al., 2024a). Nests within a supercolony cooperatively allocate resources to optimal sites. Thus, if one portion of the supercolony was controlled, the ant population would Reproduction by numerous intercastes may enable rapid colony growth. Additionally, even if the founding queen dies, the intercastes can replace her as they can produce not only workers but also winged queens and males and intercastes. Therefore, colonies do not die but keep growing and expanding via budding. This reproductive system may contribute to the invasiveness of T. brunneus. In the Ryukyu Islands, the proportion of intercaste females within T. brunneus colonies is high (equivalent to 15%–60% of worker numbers) and increases in spring and summer but decreases in winter (Yamauchi et al., 1991; Yamane & Fukumoto, 2017). No intercastes are observed in small satellite nests, however, even in summer when their number is at a maximum (Yamauchi et al., 1991). Additionally, intercastes are not observed to forage outside the nests. The situation is similar on Hachijo Island, where T. brunneus forms supercolonies (described below): the proportion of intercastes increases 136 sex ratio in wingless queens and males can be explained by the local mate competition theory (Yamane & Fukumoto, 2017). The local mate competition theory claims that in a local mating population where males compete for females, female progenitors merit by reducing competition among their male offspring and thus reproduce more females than males. In the case of T. brunneus, wingless males would be able to easily find intercaste females in the colony and copulate multiple times without encountering natural enemies, unlike in nuptial flight by alates. Thus, too many wingless males would be a waste for the colony.
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