Gene flow among habitat patches on a fragmented landscape in the spider Argiope trifasciata (Araneae: Araneidae)

Abstract

The banded garden spider (Argiope trifasciata) is a common orb weaver of old ®eld habitats in the United States. In this study, we determined levels of genetic variability and gene¯ow among seven populations in central Pennsylvania, based on variation at eight allozyme loci. Mean heterozygosity (observed) per population was 7.5% and mean polymorphism was 39.3%, consistent with levels of variability in other arthropods. Values of G ST for the four polymorphic loci (mean G ST 0.011) suggest that gene¯ow prevents the genetic di erentiation of these populations. The average number of migrants per generation (Nm) among these populations is estimated to be 31.3. The lack of signi®cant interpopulation genetic di erentiation among these disjunct populations may result from spiderling aerial dispersal (ballooning), a more continuous distribution of suitable habitat in the past, and perhaps the use of roadside vegetation as gene¯ow corridors. On the other hand, the study populations did not exhibit isolation-by-distance, suggesting that suitable habitat in our study area is experienced as less than continuous by A. trifasciata. Thus, although A. trifasciata is an excellent ballooner, ballooning does not confer unlimited access among all populations, which suggests that ballooning may be a far less e ective means of long-distance dispersal than previously thought.

Low propensity for aerial dispersal in specialist spiders from fragmented landscapes

“…However, recent empirical investigation failed to prove the importance of ballooning in short-term colonization processes, although it was the best predictor to explain the patch occupancy resulting from long-term colonization and extinction dynamics (Bonte et al 2003b). Indirect studies of ballooning dispersal also reduce the importance of ballooning for gene flow (Ramirez & Haakonsen 1999). Apparently, ballooning is not always an effective dispersal mode between populations, more a stochastic event, certainly in patchily structured populations.…”

Contrasting patterns of genetic variation in the two sympatric geckos Gekko tawaensis and G. japonicus (Reptilia: Squamata) from western Japan, as revealed by allozyme analyses

“…In many of these studies, authors have attempted to specify major causal factors for observed genetic structures in the context of isolation history (Capula, 1996;Nielson et al, 2001), current status of populations (Reh and Seitz, 1990;Hitchings and Beebee, 1996), and ecological traits relevant to dispersal ability of the taxa in question (Ramirez and Haakonsen, 1999;Naihong et al, 2000). However, because population structures of real organisms are actually formed and maintained under the confounding effects of various biotic and abiotic factors, multiple interpretations are often inevitable for the evaluation of relative importance of a particular factor (Bossart and Prowell, 1998).…”

Population structure of the expansive wasp spider (Argiope bruennichi) at the edge of its range

“…Species with a high potential for dispersal generally display a homogeneous population structure, even over considerable distances (Slatkin 1993). In the case of orb-weaving spiders, whose dispersal capabilities are usually very high, a similarly high level of gene flow can often be observed among populations (Ramirez & Fandino 1996;Ramirez & Haakonsen 1999;Lee et al 2004;Jung et al 2006). Many studies have investigated genetic differentiation among populations of spiders (e.g., Ramirez & Fandino 1996;Ramirez & Haakonsen 1999;Lee et al 2004;Jung et al 2006;Croucher et al 2011;Krehenwinkel et al 2016b), but the balance between genetic drift and migration at the margins of a species' range is still poorly understood.…”

“…In the case of orb-weaving spiders, whose dispersal capabilities are usually very high, a similarly high level of gene flow can often be observed among populations (Ramirez & Fandino 1996;Ramirez & Haakonsen 1999;Lee et al 2004;Jung et al 2006). Many studies have investigated genetic differentiation among populations of spiders (e.g., Ramirez & Fandino 1996;Ramirez & Haakonsen 1999;Lee et al 2004;Jung et al 2006;Croucher et al 2011;Krehenwinkel et al 2016b), but the balance between genetic drift and migration at the margins of a species' range is still poorly understood. Krehenwinkel & Tautz (2013) and Krehenwinkel et al (2015) examined the genetic variability in native and invasive populations of the ''wasp spider'' Argiope bruennichi (Scopoli, 1772), revealing marked distinctions between them.…”