Previous | Next

To test whether the mountaintop spider populations were diverging in more than just appearance, Masta and Maddison paired females from one mountaintop with males from a different locale. They watched to see how long it took the female to accept the male ("latency time"), starting from when the male began to dance. If the dance or the appearance of the male was not highly acceptable, they reasoned, it would take the female longer to accept the male than it would for her to accept a male from her own mountain home.

In one of the inter-mountain pairings (Galiuro x Santa Ritas), the latency time was significantly greater than for within-range pairings. In the other two (Galiuro x Sierritas and Sierritas x Santa Ritas) the differences were not significant.

As another measure of differentiation, the researchers recorded the number of viable offspring that resulted from these pairings. In two out of the three inter-mountain pairings (Galiuros x Santa Ritas and Galiuros x Sierritas), the number of offspring was significantly less than those resulting from within-range pairings.

Left: latency time. Right: viable offspring. Click on image for larger (8kb) image and detailed caption.

The fact that differences occurred in some inter-mountain pairings but not in others indicates that the process of splitting into different species is underway, but is not yet complete.

Image from Masta, S.E. and W.P. Maddison. 2002. Sexual selection driving diversification in jumping spiders. Proc. Natl. Acad. Sci. U.S.A., Vol. 99, Issue 7, 4442-4447, April 2, 2002.

Copyright © 2002 National Academy of Sciences, U.S.A. All rights reserved.