Phenological responses to climate warming in temperate moths and butterflies: species traits predict future changes in voltinism

Changes in the number of generations per year (voltinism) have been among
the most common phenological responses to climate warming in insects
inhabiting seasonal environments. Nevertheless, numerous species have
maintained univoltine (one generation per year) phenology with increasing
temperatures, indicating the involvement of phylogenetic, ecological or
some other constraints on phenological change. I examined geographic
variation in voltinism in moths and butterflies of Northern Europe to
identify species traits that might predispose species to
univoltine/multivoltine phenology. I focused on species with a wide
latitudinal distribution range (15 degrees as a minimum) which makes it
unlikely that constraints imposed by season length could preclude
multivoltinism across their distribution. Almost half of the 731 moth and
butterfly species considered appear to have a single generation throughout
their entire European range. A univoltine life-cycle across a wide
latitudinal gradient suggests the presence of some constraint that makes
additional generations either impossible or at least strongly
disadvantageous, which will unlikely change with future climate warming.
The scattered distribution of univoltine and multivoltine species across
the lepidopteran phylogeny indicates that phylogenetic constraints are not
strongly limiting changes in voltinism, and the trait is open to
ecologically-driven adaptive evolution. My data show that species with one
generation per year are generally larger than multivoltine species, but
size forms no absolute constraint to having multiple generations per year.
Obligately univoltine species dominate among egg and adult overwinterers
(life-histories typical of so-called spring-feeders), whereas species with
capacity for multiple generations prevail among pupal overwinterers.
Multivoltinism is also infrequent among species feeding on grasses,
particularly in endophagous grass-feeders. Larval diet breadth has no
discernible effect on voltinism. Given the diverse ecological consequences
of voltinism and its changes, accounting for the species’ capacity for
multivoltinism may be a key to address future challenges in biodiversity
conservation and pest management.