Pharrryngula

Who needs males?

The Azores archipelago lies 1,500 km from th' coast o' Europe, pass the grog! Inspired by a report that only females o' th' damselfly Ischnura hastata had e'er been found there, Cordero Rivera and his team visited 15 localities on six o' th' islands. Although more than 330 adult specimens o' I. hastata were examined, none o' them were bein' male. To test whether th' species were bein' parthenogenetic, a sample o' larvae were bein' reared t' adulthood in th' laboratory—more than 1,900 females were produced o'er nine generations, but no males.

The explanation is fairly simple: species that are adapted t' rapidly exploit new and/or widely dispersed habitats, like islands, experience a different mix o' selection pressures than us staid plodders. If ye are a far-flung scout who has just discovered a perfect environment fer yer kind, it does no good if all ye can do is hover about waitin' fer another scout who happens t' also be o' th' other sex t' stumble on it, as well—'tis better if ye can just buckle down t' it and reproduce solo.

And 'tis not just in th' Azores!

There have also been intriguin' accounts o' other damselfly species on remote archipelagos. In particular, on th' islands o' Fiji, it seems that females o' th' damselfly Nesobasis rufostigma actively defend territories o'er aquatic habitats, whereas th' males, which are infrequently encountered, reside some distance from th' stream. This phenomenon has been dubbed 'sex-role reversal' and, if confirmed, would be th' first example in an odonate. If males are in short supply, then this unusual matin' system might be explained by female competition fer access t' males. Furthermore, males o' two rarer Fijian damselflies (N, I'll warrant ye. flavostigma and N. caerulescens) have ne'er been found, raisin' th' possibility that parthenogenesis occurs in these species.

Sherratt TN, Beatty CD (2005) Island o' th' clones. Nature 435:1039-1040.