Genetic architecture and phenotypic plasticity of thermally-regulated traits in an eruptive species, Dendroctonus ponderosae

Abstract

Phenotypic plasticity in thermally-regulated traits enables close tracking of changing environmental conditions, and can thereby enhance the potential for rapid population increase, a hallmark of outbreak insect species. In a changing climate, exposure to conditions that exceed the capacity of existing phenotypic plasticity may occur. Combining information on genetic architecture and trait plasticity among populations that are distributed along a latitudinal cline can provide insight into how thermally-regulated traits evolve in divergent environments and the potential for adaptation. Dendroctonus ponderosae feed on Pinus species in diverse climatic regimes throughout western North America, and show eruptive population dynamics. We describe geographical patterns of plasticity in D. ponderosae development time and adult size by examining reaction norms of populations from multiple latitudes. The relative influence of additive and non-additive genetic effects on population differences in the two phenotypic traits at a single temperature is quantified using line-cross experiments and joint-scaling tests. We found significant genetic and phenotypic variation among D. ponderosae populations. Simple additive genetic variance was not the primary source of the observed variation, and dominance and epistasis contributed greatly to the genetic divergence of the two thermally-regulated traits. Hybrid breakdown was also observed in F 2 hybrid crosses between northern and southern populations, further indication of substantial genetic differences among clinal populations and potential reproductive isolation within D. ponderosae. Although it is unclear what maintains variation in the life-history traits, observed plasticity in thermally-regulated traits that are directly linked to rapid numerical change may contribute to the outbreak nature of D. ponderosae, particularly in a changing climate.

Seasonal flight patterns of Ips typographus in southern Sweden and thermal sums required for emergence

“…The required thermal sums for flight, development and emergence have been shown to differ between regions as an adaptation to local conditions (Netherer & Pennerstorfer 2001;Bentz et al 2001Bentz et al , 2011. Thermal sums for the developmental stages of I. typographus in southern Sweden are, however, unavailable, and information on seasonal flight patterns here is also sparse (Trägårdh, 1939;Eidmann and Klingström, 1990).…”

Linking embryonic temperature with adult reproductive investment in Atlantic salmon Salmo salar

“…The expression of fitness-related traits often exhibits clinal variation along latitudinal gradients, although the mechanisms allowing the variations remain obscure and have been ascribed to both phenotypic plasticity and genetic adaptation and combinations thereof (Sgrò & Blows 2004, Lardies & Bosinovic 2008, Fischer & Karl 2010, Bentz et al 2011). In our experiment, genetic adaptation appears unlikely, as the observed changes occurred within 1 generation, and we do not think that the small difference in mortality (8%) between the 2 egg incubation temperatures in the study tanks can have caused the observed changes in life-history traits.…”

Individual-Based Modeling: Mountain Pine Beetle Seasonal Biology in Response to Climate

“…6.6n) and mean temperature combined to generate a strong aridity gradient, undoubtedly a factor involved in limiting MPB population growth rates in the southern proportion of the insect's range. Also, MPB developmental responses to temperature in the southwest United States differ from those in the northern part of the insect's range (Bentz et al 2011b) from which our model parameters were obtained. Therefore, model predictions are less reliable in these areas.…”

“…The MPB is currently active in high elevation pine forests of southern Arizona. Genetic differences in developmental parameters between northern and southern populations (Bentz et al 2011b;Bracewell et al 2010), however, limit using the current model to predict MPB invasiveness in the south. Additional processes such as phloem drying in response to aridity (Cole 1981), and developmental parameters specific to southern MPB populations, will allow for a comprehensive tool to predict MPB invasiveness across the range of pines.…”