HABITAT PERSISTENCE UNDERLIES INTRASPECIFIC VARIATION IN THE DISPERSAL STRATEGIES OF PLANTHOPPERS

Dispersal is considered a vital life history characteristic for insect s exploiting temporary habitats, and life history theorists have often hypothesized an inverse relationship between dispersal capability and habitat persistence. Most often, this hypothesis has been tested usin g interspecific comparisons of dispersal capability and qualitative es timates of habitat persistence. Consequently, most assessments have fa iled to control for possible phylogenetic nonindependence and they als o lack quantitative rigor. We capitalized on existing intraspecific va riation in the dispersal capability of Prokelisia planthoppers to exam ine the relationship between habitat persistence and dispersal, thereb y minimizing possible phylogenetic effects. Two congeneric species (Pr okelisia marginata and P. dolus) occur in the intertidal marshes of No rth America, where they feed exclusively on cordgrasses (Spartina). Be cause these planthoppers exhibit wing dimorphism, flight-capable adult s (macropters with fully developed wings) are easily differentiated fr om flightless adults (brachypters with reduced wings). Thus, dispersal capability can be readily estimated by the percentage of macropters i n a population. At a regional spatial scale, we found a highly signifi cant negative relationship between dispersal capability (percent macro ptery) and habitat persistence. In this system, habitat persistence is influenced by a combination of marsh elevation, winter severity, and tidal range, which interact to determine the ability of planthoppers t o endure through winter in their primary habitat for development. P. m arginata develops primarily in low-marsh habitats during summer, habit ats that can be subjected to pronounced winter disturbance due to ice scouring and/or extensive tidal inundation. Levels of winter disturban ce of the low marsh are extreme along the Atlantic coast, intermediate along the Pacific, and low along the Gulf. Both the failure of P. mar ginata populations to remain through winter in this habitat, and the d ispersal ability of these populations (92%, 29%, and 17% macroptery, r espectively), are correlated with levels of disturbance. Thus, in regi ons where winter disturbance is high, levels of dispersal are correspo ndingly high to allow for recolonization of extirpated habitats from o verwintering sites on the high marsh. Unlike P. marginata, P. dolus de velops primarily in high-marsh habitats, which are much less disturbed on all coasts during winter. Consequently, this species remains year- round in its primary habitat for development, and most populations exh ibit relatively low levels of macroptery (<10%). When raised under com mon garden conditions, many more macropters of both species were produ ced from Atlantic compared to Gulf populations. Thus the proportion of macropters produced from the populations used in this experiment para lleled the incidence of macroptery measured in the field, providing ev idence that the geographic variation in dispersal capability in both s pecies has in part a genetic basis. The results of this study provide strong intraspecific evidence for an inverse relationship between the dispersal capability of insects and the persistence of their habitats.