Abstract
Allochrony that is reproductive isolation by time may further lead to divergence of reproductive adaptive traits in response to different environmental pressures over time. A unique “summer” population of the pine processionary moth Thaumetopoea pityocampa, reproductively isolated from the typical winter populations by allochronic differentiation, is here analyzed. This allochronically shifted population reproduces in the spring and develops in the summer, whereas “winter” populations reproduce in the late summer and have winter larval development. Both summer and winter populations coexist in the same pine stands, yet they face different climatic pressures as their active stages are present in different seasons. The occurrence of significant differences between the reproductive traits of the summer population and the typical winter populations (either sympatric or allopatric) is thus hypothesized. Female fecundity, egg size, egg covering, and egg parasitism were analyzed showing that the egg load was lower and that egg size was higher in the summer population than in all the studied winter populations. The scales that cover the egg batches of T. pityocampa differed significantly between populations in shape and color, resulting in a looser and darker covering in the summer population. The single specialist egg parasitoid species of this moth was almost missing in the summer population, and the overall parasitism rates were lower than in the winter population. Results suggest the occurrence of phenotypic differentiation between the summer population and the typical T. pityocampa winter populations for the life-history traits studied. This work provides an insight into how ecological divergence may follow the process of allochronic reproductive isolation.
Highlights
Understanding the genetic, phenotypic, and ecological differentiation occurring during speciation processes is most relevant in evolutionary biology studies
Ecology and Evolution published by John Wiley & Sons Ltd
We considered a latitudinal cline based on findings of Pimentel et al (2010), who reported that, in T. pityocampa, fecundity increases and egg size decreases with increasing latitude
Summary
Understanding the genetic, phenotypic, and ecological differentiation occurring during speciation processes is most relevant in evolutionary biology studies. Even when genetic mutations occur, subsequent ecological divergence due to different environmental pressures is important to complete speciation (Coyne and Orr 1998; Turelli et al 2001; Nosil et al 2009; Schluter 2009; Matsubayashi et al.2010). According to the theory of ecological speciation, factors such as food availability, shelter, intraspecific competition, climate and predators can act as determinant selection pressures in the processes through which populations diverge and eventually become new species (Ridley 2004). Either geographical or ecological barriers commonly lead to disruption of the gene flow, causing the resulting populations to evolve under different selection pressures, so that speciation can occur as a by-product of ecological adaptation
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