Sexual size dimorphism (SSD) is widespread among diverse animal taxa and has attracted the attention of evolutionary biologists for over a century. SSD is likely to be adaptive and the result of divergent selection on different size optima for males and females, given their different roles in reproduction. The developmental trajectory leading to SSD may help us to understand how selection acts on male and female size. Here, we describe the growth and development of two Australian praying mantids, Pseudomantis albofimbriata and Hierodula majuscula including the number of moults, time to adulthood, size at each moult, and the degree of SSD. While both species exhibit the common pattern of female-biased SSD, the number of moults required for individuals to reach adulthood differed between males and females and between species. Despite their larger adult size, P. albofimbriata females require fewer moults and less time than males to reach adulthood, but are significantly larger than males from the second instar onwards. In contrast, H. majuscula males reached adulthood in fewer moults, and less time than females, however males and females did not differ in size until females went through their final moult into adulthood. H. majuscula also required more time and more moults to reach adulthood than P. albofimbriata. We discuss these different developmental pathways in light of the existing knowledge of reproductive biology for each species. We also suggest that these differences may relate to the different phenologies that occur in strongly seasonal temperate environments compared with those in the tropics. This study provides evidence that SSD can result from two different patterns of growth and development in closely related species.

Many sensory modes can be exploited to determine the location of potential mates. In insects, long-distance location primarily involves chemical or acoustic cues, whereas short-distance communication mainly utilises visual or tactile cues. The structural complexity of the environment may influence the transmission of information, and therefore, it is common to see multiple sensory modes employed to increase the likelihood of accurate mate location. Praying mantids are known to use airborne chemicals for long-distance location and visual cues in close proximity. This study examined which types of cues are used for mate location in an unstudied species, Hierodula majuscula, from Queensland, Australia. The timing of female pheromone emission during calling periods reached a peak at 3:00 h, with the majority of females assuming a calling posture at this time. Scanning electron microscopy was used to confirm the presence of basiconic sensilla (used for chemical reception) on male antennae, and males successfully responded to female chemical cues and subsequently located potential mates. Males were not as successful at finding females when restricted to using visual cues.

Sperm competition occurs when a female mates with more than one male, and the sperm of those males compete directly over fertilizing her eggs. In polyandrous animals, males can respond to the perceived risk of sperm competition by flexibly adjusting aspects of their development and reproductive investment. In high-risk scenarios we might expect males to accelerate development so as to mature quickly and locate receptive females first and/or transfer more sperm so as to outcompete rival sperm. We examined these predictions using the false garden mantid, Pseudomantis albofimbriata, a medium-sized praying mantid found on the east coast of Australia. Males are less than half the mass of females. Sexual cannibalism occurs in up to 40% of interactions, highlighting the importance of investing optimally in reproductive opportunities for males. We housed juvenile males in two operational sex ratio treatments: three males, one female ( high risk of sperm competition) and one male, three females ( low risk). We found no evidence of accelerated development in the high-risk group; instead, high-risk males took longer to mature. Possibly, males exposed to a higher risk of sperm competition delay maturity in order to invest in testes development and sperm production. We also found that males reared in the high-risk treatment transferred significantly more sperm than males reared in the low-risk treatment, providing evidence of strategic ejaculation in male P. albofimbriata. This is the first study demonstrating a male response to the perceived risk of sperm competition via delayed development and increased ejaculate investment in praying mantids. Crown Copyright (C) 2011. Published on behalf of The Association for the Study of Animal Behaviour by Elsevier Ltd. All rights reserved.