Seeing the world through the eyes of a butterfly: visual ecology of the territorial males of Pararge aegeria (Lepidoptera: Nymphalidae)

Combining studies of animal visual systems with exact imaging of their visual environment can get us a step closer to understand how animals see their “Umwelt”. Here, we have combined both methods to better understand how males of the speckled wood butterfly, Pararge aegeria, see the surroundings of their perches. These males are well known to sit and wait for a chance to mate with a passing females, in sunspot territories in European forests. We provide a detailed description of the males' body and head posture, viewing direction, visual field and spatial resolution, as well as the visual environment. Pararge aegeria has sexually dimorphic eyes, the smallest interommatidial angles of males are around 1°, those of females 1.5°. Perching males face the antisolar direction with their retinal region of the highest resolution pointing at an angle of about 45° above the horizon; thus, looking at a rather even and dark background in front of which they likely have the best chance to detect a sunlit female passing through the sunspot.

Ecological Analysis of Butterflies and Day-Flying Moths Diversity of the Gouraya National Park (Algeria)

This work represents an initial analysis of butterflies and day-flying moths of the Gouraya National Park (Algeria). Forty-eight field-surveys were made between February 2011 and January 2012, in three stations (the cliff, the low matorral and the high matorral). It allowed us to identify 38 species, belonging to 6 families: Lycaenidae (13 species), Nymphalidae (10 species), Pieridae (9 species), Papilionidae (2 species), Hesperiidae (2 species), Zygaenidae (1 species) and Sphingidae (1 species). The low matorral and cliff were the richest stations, with 33 species for the first one and 23 species for the latter. Only seven species were observed in the high matorral where the highest centesimal frequency was recorded for the Pararge aegeria (47.83 %). This species records the highest frequency of occurrences in all 3 stations. The low matorral (H' = 4.25 bits, E = 0.84) proved to be the most diversified and balanced station.

Watching the days go by: asymmetric regulation of caterpillar development by changes in photoperiod

Many insects possess the plastic ability to either develop directly to adulthood, or enter diapause and postpone reproduction until the next year, depending on environmental cues (primarily photoperiod) that signal the amount of time remaining until the end of the growth season. These two developmental pathways often differ in co-adapted life history traits, e.g. with slower development and larger size in individuals headed for diapause. The developmental timing of these differences may be of adaptive importance: if pathways diverge late, the scope for phenotypic differences is smaller, whereas if pathways diverge early, the risk is higher of expressing a maladaptive phenotype if the selective environment changes. Here we explore the effects of changes in photoperiodic information during life on pupal diapause and associated life history traits in the butterfly Pararge aegeria. We find that both pupal diapause and larval development rate are asymmetrically regulated: while exposure to long days late in life (regardless of earlier experiences) was sufficient to produce nondiapause development and accelerate larval development accordingly, more prolonged exposure to short days was required to induce diapause and slow down pre-diapause larval development. While the two developmental pathways diverged early in development, development rates could be partially reversed by altered environmental cues. Meanwhile, pathway differences in body size were more inflexible, despite emerging late in development. Hence, in P. aegeria several traits are regulated by photoperiod, along subtly different ontogenies, into an integrated phenotype that strikes a balance between flexibility and phenotype-environment matching.

Wing morphological responses to latitude and colonisation in a range expanding butterfly

Populations undergoing rapid climate-driven range expansion experience distinct selection regimes dominated both by increased dispersal at the leading edges and steep environmental gradients. Characterisation of traits associated with such expansions provides insight into the selection pressures and evolutionary constraints that shape demographic and evolutionary responses. Here we investigate patterns in three components of wing morphology (size, shape, colour) often linked to dispersal ability and thermoregulation, along latitudinal gradients of range expansion in the Speckled Wood butterfly (Pararge aegeria) in Britain (two regions of expansion in England and Scotland). We measured 774 males from 54 sites spanning 799 km with a 10-year mean average temperature gradient of 4 °C. A geometric morphometric method was used to investigate variation in size and shape of forewings and hindwings; colour, pattern, and contrast of the wings were examined using a measure of lightness (inverse degree of melanism). Overall, wing size increased with latitude by ∼2% per 100 km, consistent with Bergmann’s rule. Forewings became more rounded and hindwings more elongated with history of colonisation, possibly reflecting selection for increased dispersal ability. Contrary to thermal melanism expectations, wing colour was lighter where larvae developed at cooler temperatures and unrelated to long-term temperature. Changes in wing spot pattern were also detected. High heterogeneity in variance among sites for all of the traits studied may reflect evolutionary time-lags and genetic drift due to colonisation of new habitats. Our study suggests that temperature-sensitive plastic responses for size and colour interact with selection for dispersal traits (wing size and shape). Whilst the plastic and evolutionary responses may in some cases act antagonistically, the rapid expansion of P. aegeria implies an overall reinforcing effect between these two mechanisms.

Analyzing the neutral and adaptive background of butterfly voltinism reveals structural variation in a core circadian gene

ABSTRACTMany insects exhibit geographic variation in voltinism, the number of generations produced per year. This includes high-latitude species in previously glaciated areas, implying divergent selection on life cycle traits during or shortly after recent colonization. Here, we use a whole-genome approach to genetically characterize a set of populations of the butterfly Pararge aegeria that differ in voltinism. We construct a high-quality de novo genome for P. aegeria, and assess genome-wide genetic diversity and differentiation between populations. We then use the inferred phylogeographic relationships as the basis for a scan for loci showing signs of divergent selection associated with voltinism differences. The genic outliers detected include population-specific mutations of circadian loci, most notably a locally fixed 97-amino acid deletion in the circadian gene timeless. Variation in timeless has previously been implicated as underlying variation in life cycle regulation in wild populations in our study species, as well as in other insects. These results add to a growing body of research framing circadian gene variation as a mechanism for generating local adaptation of life cycles.

Vertically transmitted rhabdoviruses are found across three insect families and have dynamic interactions with their hosts

A small number of free-living viruses have been found to be obligately vertically transmitted, but it remains uncertain how widespread vertically transmitted viruses are and how quickly they can spread through host populations. Recent metagenomic studies have found several insects to be infected with sigma viruses ( Rhabdoviridae ). Here, we report that sigma viruses that infect Mediterranean fruit flies ( Ceratitis capitata ), Drosophila immigrans , and speckled wood butterflies ( Pararge aegeria ) are all vertically transmitted. We find patterns of vertical transmission that are consistent with those seen in Drosophila sigma viruses, with high rates of maternal transmission, and lower rates of paternal transmission. This mode of transmission allows them to spread rapidly in populations, and using viral sequence data we found the viruses in D. immigrans and C. capitata had both recently swept through host populations. The viruses were common in nature, with mean prevalences of 12% in C. capitata , 38% in D. immigrans and 74% in P. aegeria . We conclude that vertically transmitted rhabdoviruses may be widespread in a broad range of insect taxa, and that these viruses can have dynamic interactions with their hosts.

Vertically transmitted rhabdoviruses are found across three insect families and have dynamic interactions with their hosts

A small number of free-living viruses have been found to be obligately vertically transmitted, but it remains uncertain how widespread vertically transmitted viruses are and how quickly they can spread through host populations. Recent metagenomic studies have found several insects to be infected with sigma viruses (Rhabdoviridae). Here, we report that sigma viruses that infect Mediterranean fruit flies (Ceratitis capitata),Drosophila immigrans, and speckled wood butterflies (Pararge aegeria) are all vertically transmitted. We find patterns of vertical transmission that are consistent with those seen inDrosophilasigma viruses, with high rates of maternal transmission, and lower rates of paternal transmission. This mode of transmission allows them to spread rapidly in populations, and using viral sequence data we found the viruses inD. immigransandC. capitatahad both recently swept through host populations. The viruses were common in nature, with mean prevalences of 12% inC. capitata,38% inD. immigransand 74% inP. aegeria. We conclude that vertically transmitted rhabdoviruses may be widespread in insects, and that these viruses can have dynamic interactions with their hosts.