Not so woollen Jumpers

Subbing this morning and teaching this evening, so here's a few shots from warmer times:

Admirable Jumper (Hentzia palmarum), Ilinois Beach SP, Lake Co, IL 9/15/2012

Bronze Jumper (Eris militaris), Nicolet NF, Oconto Co, WI  8/11/2013

Tutelina elegans, Lyons Woods FP, Lake Co, IL  7/1/2013

 

These are all Jumping Spiders, in the family Salticidae. (Although they look rather fearsome, especially the long front legs on that Admirable Jumper, very few species get longer than a centimeter, and most are quite a bit smaller. These are little, tiny, harmless guys.) They are the most diverse family of spiders, with approximately 5000 species. Approximately 300 of those live in the US and Canada.

 

One reason I really like these guys, I have to admit, is those big medial eyes -- you can actually see them looking at you! And in contrast to most spiders, they really can see you. Their eyes can actually focus well out in front of them, which many spiders can't, and they have excellent color vision, with three different layers of photoreceptors each apparently targeting a different wavelength. (There's a fourth layer that appears to work quite differently, perhaps detecting polarization.) (1) Short eyes, inevitable in such a small critter, do have issues with focal length, but these guys actually use pits in their retinas to extend their focus. In other words, their main eyes are the equivalent of a 75mm. camera lens! (2) Their visual system is similar enough to ours in function (not in structure) that they can actually observe, and be fooled by, video images. (3)

 

Masta and Maddison used this ability to examine sexual selection in these spiders. As you can see from the photos, some Jumping Spiders are quite striking visually, and many species show distinct sexual dimorphism. As it turns out, (and as we might expect), sexual selection based in part on visual signals appears to be driving the evolution of different populations in Habronattus pugillis. (4) Given the extent of dimorphism and the impressive diversity in these spiders, it's likely that this pattern is widespread, and sexual selection may be a big part of how this big family of little critters got so big in the first place.

 

 

Land, M. F. (1969). Structure of the retinae of the principal eyes of jumping spiders (Salticidae: Dendryphantinae) in relation to visual optics. Journal of experimental biology, 51(2), 443-470.

 

Williams, D. S., & MeIntyre, P. (1980). The principal eyes of a jumping spider have a telephoto component.

 

Clark, D. L., & Uetz, G. W. (1990). Video image recognition by the jumping spider,< i> Maevia inclemens</i>(Araneae: Salticidae). Animal Behaviour, 40(5), 884-890.

 

Masta, S. E., & Maddison, W. P. (2002). Sexual selection driving diversification in jumping spiders. Proceedings of the National Academy of Sciences, 99(7), 4442-4447.