The roles of geography and founder effects in promoting host‐associated differentiation in the generalist bogus yucca moth Prodoxus decipiens

Abstract

There is ample evidence that host shifts in plant-feeding insects have been instrumental in generating the enormous diversity of insects. Changes in host use can cause host-associated differentiation (HAD) among populations that may lead to reproductive isolation and eventual speciation. The importance of geography in facilitating this process remains controversial. We examined the geographic context of HAD in the wide-ranging generalist yucca moth Prodoxus decipiens. Previous work demonstrated HAD among sympatric moth populations feeding on two different Yucca species occurring on the barrier islands of North Carolina, USA. We assessed the genetic structure of P. decipiens across its entire geographic and host range to determine whether HAD is widespread in this generalist herbivore. Population genetic analyses of microsatellite and mtDNA sequence data across the entire range showed genetic structuring with respect to host use and geography. In particular, genetic differentiation was relatively strong between mainland populations and those on the barrier islands of North Carolina. Finer scale analyses, however, among sympatric populations using different host plant species only showed significant clustering based on host use for populations on the barrier islands. Mainland populations did not form population clusters based on host plant use. Reduced genetic diversity in the barrier island populations, especially on the derived host, suggests that founder effects may have been instrumental in facilitating HAD. In general, results suggest that the interplay of local adaptation, geography and demography can determine the tempo of HAD. We argue that future studies should include comprehensive surveys across a wide range of environmental and geographic conditions to elucidate the contribution of various processes to HAD.

Geography is more important than host plant use for the population genetic structure of a generalist insect herbivore

“…We performed genetic analyses on two separate sets of samples to address our three goals. To address part of our first goal (the extent of genetic divergence between the two types) and the second goal, we used black and red FW over a 250–3,000 km range; thus, we define this data set as “broad geographic scale.” To address our third goal, we used samples of red FW collected in Colorado over a range of 40–700 km; thus, we define this data set as “fine geographic scale.” We analysed the broad and fine geographic scale data sets separately because we only had reliable within‐population diet breadth data for Colorado, which has only red populations, and because patterns may vary depending on the geographic scale being analysed (e.g., Darwell et al, ). The broad‐scale data set included 61 samples (41 of red, 20 of black) from a 3,000‐km longitudinal transect, and the fine‐scale data set included 126 samples of red FW only from Colorado.…”

“…To address our third goal, we used samples of red FW collected in Colorado over a range of 40-700 km; thus, we define this data set as "fine geographic scale." We analysed the broad and fine geographic scale data sets separately because we only had reliable within-population diet breadth data for Colorado, which has only red populations, and because patterns may vary depending on the geographic scale being analysed (e.g., Darwell et al, 2014). The broad-scale data set included 61 samples (41 of red, 20 of black) from a 3,000-km longitudinal transect, and the fine-scale data set included 126 samples of red FW only from Colorado.…”

“…Geographic structure and isolation of populations are thought to play important roles in the diversification of herbivorous insects for both adaptive and nonadaptive macroevolutionary hypotheses (Hardy, Peterson, & Normark, 2016;Janz & Nylin, 2008). Indeed, geographic distance has been shown to influence host plant-related population differentiation of bogus yucca moths (Darwell, Fox, & Althoff, 2014). Isolation by distance has long been advocated as an important factor fostering evolutionary change in many species (Wright, 1943), as gene flow is expected to be negatively correlated with geographic distance.…”

Host‐associated differentiation in a highly polyphagous, sexually reproducing insect herbivore

“…Level of intimacy with their hosts (i.e., whether an insect lives/feeds within plant tissues vs. externally) and the type of reproduction (i.e., sexual or asexual) are factors thought to influence the propensity of insects to exhibit HAD (Medina 2012). Much of what we know about HAD involves insect species with narrow host ranges (i.e., specialists) that spend part or all their life cycle inside their hosts, and/or reproduce asexually (e.g., parthenogenetically) (Pashley 1986;Van Zandt and Mopper 1998;Brunner et al 2004;Medina 2010, 2012;Cook et al 2012;Darwell et al 2014;Marques et al 2014). Pea aphids, for example, are parthenogenetic Fabaceae specialists that are composed of genetically distinct host-associated lineages on clover and alfalfa (Via 1999).…”

The interaction between diet breadth, geography and gene flow in herbivorous insects

“…Aleurocanthus spiniferus Wang et al (2015) 10.1016/j.gene.2015.01.050 None. Darwell et al (2014) Raymond et al (2013) 10.1111/mec.12483 Poor host records. Weighted host specificity based on host plant order only.…”