Dispersal and life history of brown widow spiders in dated invasive populations on two continents

Theory and empirical work suggest that behaviours such as dispersal and exploration are predictors of invasive success, and that behaviours may shift predictably after invasive populations have established and spread. However, there are limited data on temporal patterns in the distribution of behavioural traits linked to the timeline of establishment of invasive species. We examined dispersal and exploration, along with life history traits that may be linked to behaviour, across multiple invasive populations of the brown widow spider, Latrodectus geometricus. This global invader has established populations across the United States and Israel. Using this temporal and spatial variation, we tested predictions about changes in suites of traits over establishment time. We compared trait distributions of four U.S. populations of L. geometricus to patterns in four populations in Israel. We predicted that selective filters during the invasion process would result in more dispersive, more exploratory spiders that are larger and more fecund in recently established populations, but, if trade-offs occur, dispersal would be favoured at the expense of fecundity and size in recent populations. We found more frequent and faster dispersal in more recently established populations in Israel, but not the United States. Spiders in more recently established populations in Israel were larger than those in older populations, but there were no consistent patterns across U.S. populations. However, there was evidence in both the U.S. and Israel for differing trade-offs among fecundity, dispersal and size. In more recently established populations, spiders were more variable in resource allocation to eggsacs. The results suggest that in some populations, trade-offs underlying dispersal, fecundity and body size are shaped by the time interval, and thus the number of generations, since establishment, with implications for the role of evolutionary processes in invasion success.