Geographic parthenogenesis and the common tea-tree stick insect of New Zealand

Abstract

Worldwide, parthenogenetic reproduction has evolved many times in the stick insects (Phasmatidae). Many parthenogenetic stick insects show the distribution pattern known as geographic parthenogenesis, in that they occupy habitats that are at higher altitude or latitude compared with their sexual relatives. Although it is often assumed that, in the short term, parthenogenetic populations will have a reproductive advantage over sexual populations; this is not necessarily the case. We present data on the distribution and evolutionary relationships of sexual and asexual populations of the New Zealand stick insect, Clitarchus hookeri. Males are common in the northern half of the species' range but rare or absent elsewhere, and we found that most C. hookeri from putative-parthenogenetic populations share a common ancestor. Female stick insects from bisexual populations of Clitarchus hookeri are capable of parthenogenetic reproduction, but those insects from putative-parthenogenetic populations produced few offspring via sexual reproduction when males were available. We found similar fertility (hatching success) in mated and virgin females. Mated females produce equal numbers of male and female offspring, with most hatching about 9-16 weeks after laying. In contrast, most eggs from unmated females took longer to hatch (21-23 weeks), and most offspring were female. It appears that all C. hookeri females are capable of parthenogenetic reproduction, and thus could benefit from the numerical advantage this yields. Nevertheless, our phylogeographic evidence shows that the majority of all-female populations over a wide geographic area originate from a single loss of sexual reproduction.

Fire and slice: palaeogeography for biogeography at New Zealand's North Island/South Island juncture

“…Furthermore, observations from intraspecific animal phylogeography support the inference of recent occupation of the region (e.g. stick insects, Buckley et al 2009;Morgan-Richards et al 2010), and recent bridging of Cook Strait (e.g. Hemideina tree weta, Galaxiid fish, Paranephrops freshwater crayfish; see Wallis & Trewick 2009) is also consistent with young landscape formation and connection (Fig.…”

The geography of sex: sexual conflict, environmental gradients and local loss of sex in facultatively parthenogenetic animals

“…Second, rare males in female-biased populations should exhibit exaggerated coercive traits compared with males from unbiased populations. While there is some anecdotal support for these predictions [29,30,65–67], more empirical data are needed. For example, large parts of the southern range of the New Zealand common tea-tree stick insect have no males, and females from these populations perform poorly when crossed with males from northern regions [29], suggesting higher resistance to fertilization in more female-biased habitats.…”

“…Like obligately sexual and asexual sister taxa, some facultatively parthenogenetic organisms exhibit spatial variation in sex ratio along environmental gradients. For example, in the common tea-tree stick insect, Clitarchus hookeri , from New Zealand, equal sex ratios are found on the west coast of the North Island but sex ratios become increasingly female-biased towards the east, culminating in all-female populations on the South Island where the species' range appears to be expanding [29]. Interestingly, when South Island females are crossed with North Island males, far fewer sons are produced [29], suggesting an association between high rates of parthenogenesis and increased fertilization failure or resistance.…”

“…For example, in the common tea-tree stick insect, Clitarchus hookeri , from New Zealand, equal sex ratios are found on the west coast of the North Island but sex ratios become increasingly female-biased towards the east, culminating in all-female populations on the South Island where the species' range appears to be expanding [29]. Interestingly, when South Island females are crossed with North Island males, far fewer sons are produced [29], suggesting an association between high rates of parthenogenesis and increased fertilization failure or resistance. Intriguingly, in two species of facultatively parthenogenetic Japanese harvestmen, Leiobunum manubriatum and Leiobunum globosum , males decline in number with increasing latitude and altitude [30], but males from the most female-biased populations exhibit exaggerated secondary sexual traits that are used for mate clasping and copulation [30].…”

Facultative sex and reproductive strategies in response to male availability in the spiny stick insect, Extatosoma tiaratum

“…This explanation assumes that the prospects of sexually produced eggs are greater than that of asexually produced eggs, for which there is some evidence in phasmatids (see Bedford 1978 for review) and other insects (e.g. Corley and Moore 1999;Kramer and Templeton 2001; but see Matsuura and Kobayashi 2007;Morgan-Richards et al 2010). Indeed, females of many insects adjust their ovipositing rates in response to environmental conditions that may affect the survival of offspring (e.g.…”