Much work has been done on the effects of urbanization, and especially light and sounds, on bird fauna. In general, the effects have been fairly striking, including more singing at “night” (because there is artificial lighting) and changes to song to make them more audible in a very competitive urban soundscape. Some work has also been on nocturnal insects, including some moths, focused especially on the deleterious impact of artificial lighting on finding mates.
Comparatively little is known, however, about the impacts of urbanization on the phenology of Lepidoptera. A recent (2021) paper in PNAS suggests a range of changes in the biology of some common leps in response to urban environments. These changes even appear to be driving evolutionary pathways.
The researchers studied two common leps in Scandinavia, the Green-veined White (Pieris napi), and the Latticed Heath (Chiasmia clathrata, a geometer moth), and their response to urbanization. The butterfly is a multivoltine species that flies throughout the season; the moth is normally bivoltine but long-flying. Both are common and regularly show up in citizen science surveys; the geometer flies by day as well as by night.
From lab experiments on the leps’ photoperiodism and phenology, the team predicted that both would emerge earlier in the season and fly later, in response to both artificially induced longer daylight early in spring and late in the summer and to warmer ambient temperatures in urban areas as compared with rural locations. In the field, these predictions held true. For P. napi for example this averaged out to urban whites flying some five days later in the season than their rural counterparts. Warmer urban sites also allow for faster development rates and longer periods of growth and reproduction than their cooler rural surroundings, the researchers noted, so the five-day difference is likely even more important than simply a longer time to fly. The difference probably also is enough to drive evolutionary changes in flight period and development.
The research “shows typically longer flight periods for both study species that end later in the season in urban areas versus their rural surroundings, suggestive of a partial extra generation,” the authors write. “From an evolutionary perspective, it is this increased voltinism that is the most important response, since an extra generation may accelerate population growth and facilitate further adaptation. Nonetheless, producing an extra generation at high latitudes also entails risks; entire cohorts may perish if winter arrives before individuals reach a stage that allows successful overwintering.”
“Altered seasonality of urban environments can lead to corresponding evolutionary changes in the seasonal responses of urban populations, a pattern that may be repeated in other species,” they conclude.
Read the full paper below in the LepLog library.
LepLog 