In the Neighbourhood of Nannenines

We’re all used to biodiversity being localized — kangaroos in Australia, tigers in Asia — but the degree of localization varies from group to group. A broader group of species may be distributed across the world (e.g. bats), even though individually each of its distinct species might have a limited range. In the case of jumping spiders, some broader groups are quite restricted. Nannenines, for instance, are only in southeast Asia, the thiratoscirtines only in Africa.

Singapore, and southeast Asia in general, is the land of nannenines. That mouthful of Ns refers to a group of species of little jumping spiders most of whom hop on the leaf litter of forests. They hold a special place in my heart, for I met them on my memorable first trip to Asia in 2005. Back in Singapore 14 years later, I was pleased to see some familiar faces. Here are two, Idastrandia and Nannenus, shown at the same scale.

Males of Idastrandia orientalis (left) and Nannenus syrphus (right), to same scale. 

From my previous sampling, there remained some puzzles. For example, in 2005 I’d found two types of male Nannenus and two types of females, but I couldn’t figure out which male matched with which female. (I could have seen which males mated with which females, but that type of behavioural experiment requires more specimens and time than I had.) Now I think I’ve figured it out by getting paired types in the same patches of leaf litter. This seems to be the pairing.

Nannenus species A (left) and B (right), with males on top and females on bottom. Yes, they look a lot alike.

Nannenines are very poorly known; there are many species that I’ve collected, but only a few have been described scientifically. Perhaps they haven’t been as well collected as other salticids because they are hidden in the dark forests.

I suspect their preference for dark humid places is also the reason they are localized to southeast Asia. For their ancestors, finding a moist and shaded path between southeast Asia and the African rainforests, for instance, was rather difficult, with habitats inhospitable to them — deserts and savannahs — intervening. Reciprocally, the thiratoscirtines of Africa are mostly isolated to the shaded rainforests, and are not known from Asia. In contrast, groups of jumping spiders that live in open sunny habitats, like the chrysillines and plexippines, are widespread across Africa, Europe, and all corners of Asia. If you want to find the unique salticids of an area, go to the humid darkness.

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