Geographical variation in wolf spider dispersal behaviour is related to landscape structure

Abstract

Theoretical studies suggest that mechanisms underlying habitat and population structure are important for shaping inter-and intraspecific variation in dispersal behaviour. Empirical evidence, especially in organisms living in spatially structured populations, however, is scarce. We investigated the relation between habitat configuration (patch size, connectivity) and dispersal by studying variation in tiptoe behaviour in the dune wolf spider, Pardosa monticola, under standardized laboratory conditions. Tiptoe behaviour prepares spiderlings for ballooning and can hence be considered as a precursor of aerial dispersal. The proportion of individuals that displayed tiptoe behaviour was highest in offspring from grasslands in a large dune landscape where habitat was continuously available, intermediate in offspring originating from a fragmented landscape, and lowest in offspring originating from a small and extremely isolated grassland patch. At the level of the fragmented landscape, variation was related to size and connectivity of four subpopulations. Both between and within landscapes, maternal condition had no effect on offspring dispersal. These results indicate that changes in habitat configuration from a large, connected landscape towards a small, fragmented one may lead to a decrease in dispersal rates, even at small spatial scales. Hence, behavioural traits narrowly linked to dispersal evolve towards less mobile phenotypes in small, isolated habitats, indicating high dispersal costs and low efficacy for gene flow in a spider species restricted to fragmented habitats.

Thermal conditions during juvenile development affect adult dispersal in a spider

“…Furthermore, plasticity in relation to thermal conditions during juvenile development appeared to be adaptive (i.e., beneficial) with respect to optimal seasonal dispersal movements. From earlier studies, we know that the costs of ballooning become higher when suitable habitat becomes scarcer, both in terms of area and isolation (15,22). Our results add to this evidence because ballooning motivation declines when spiders are exposed to temperatures that represent the season with sparsely distributed winter habitat.…”

“…Under these conditions, ballooning is an effective means of distributing individuals over a wide area of productive crop habitat. However, mortality risks are probably high for long-distance (uncontrolled) ballooning in landscapes when dispersal is toward less widespread noncrop hibernation sites (20,22). High mortality costs associated with ballooning are therefore expected to select for the adoption of more controlled, lower-risk behavior, such as rappelling.…”

“…When they rappel, spiders attach a thread to the substrate before takeoff, with the thread remaining attached while the spider bridges short distances. These behavioral components can be quantified under highly standardized laboratory conditions, making these spiders especially amenable to reaction-norm analysis (15,16,(20)(21)(22).The temperature experienced by juvenile ectotherms during development can influence their body condition and fitness (23-25) and may influence their adult life history in 2 distinct ways. First, under conditions that are suboptimal for development, inferior body condition may place a severe constraint on particular traits, including how much the animals invest in costly dispersal behaviors.…”

“…When they rappel, spiders attach a thread to the substrate before takeoff, with the thread remaining attached while the spider bridges short distances. These behavioral components can be quantified under highly standardized laboratory conditions, making these spiders especially amenable to reaction-norm analysis (15,16,(20)(21)(22).…”

Correction to ‘Adaptation to fragmentation: evolutionary dynamics driven by human influences’

“…reduction of dispersal motivation in spiders from dune grassland fragments [69]; the evolution of flightlessness in insects (woodlands, deserts, islands, etc.) [86] reduced migratory behaviour in Oncorhynchus mykiss consecutive to river isolation [87] increased dispersal: increased colonization advantage of dispersal high dispersal in Western bluebirds colonizing disturbed areas and are replaced by phylopatric bluebird along the succession (over a 20 -30 years cycle) [88]; evolution of flight-related morphology (with putative effect on dispersal) in a butterfly from recently fragmented grassland fragments [71];…”