Unravelling the genetic basis of adaptive traits is a major challenge in evolutionary biology. Doing so informs our understanding of evolution towards an adaptive optimum, the distribution of locus effect sizes, and the influence of genetic architecture on the evolvability of a trait. In the Müllerian co-mimics Heliconius melpomene and Heliconius erato some Mendelian loci affecting mimicry shifts are well known. However, several phenotypes in H. melpomene remain to be mapped, and the quantitative genetics of colour pattern variation has rarely been analysed. Here we use quantitative trait loci (QTL) analyses of crosses between H. melpomene races from Peru and Suriname to map, for the first time, the control of the broken band phenotype to WntA and identify a ~100 kb region controlling this variation. Additionally, we map variation in basal forewing red-orange pigmentation to a locus centred around the gene ventral veins lacking (vvl). The locus also appears to affect medial band shape variation as it was previously known to do in H. erato. This adds to the list of homologous regions controlling convergent phenotypes between these two species. Finally we show that Heliconius wing-patterning genes are strikingly pleiotropic among wing pattern traits. Our results demonstrate how genetic architecture can shape, aid and constrain adaptive evolution.

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Supraglacial river networks are systems of channels cut down into the surface ice of glaciers, ice sheets, and ice shelves by flowing water. They are important because the water they carry, and indeed the water that creates them, is a product of ice melt. The movement of water through these channels toward the margins of ice bodies, where it is eventually evacuated, represents the removal of mass from glaciers and ice sheets. Supraglacial river networks are highly seasonal, due to the requirement for flowing water in their creation. Here, in addition to considering their importance and temporal evolution, the entry also addresses their geometry and size, as well as the role that they play in impacting the reflectance of an ice surface, and in delivering water to subglacial locations where it can influence ice dynamics. Supraglacial river networks are relatively understudied, yet here it is shown that they are of the utmost importance in the field of glaciology.

<p>Supraglacial channels and lakes across the Greenland Ice Sheet form a key component in the routing and storage of surface meltwater during the summer melt season, yet to-date, their temporal evolution remains poorly mapped and quantified across the Greenland Ice Sheet. We produce the first high-resolution record of the seasonal supraglacial drainage network (channels and lakes) at Humboldt Glacier, northwest Greenland, spanning the melt seasons of 2016 to 2020. Using an automatic detection algorithm applied to Sentinel-2 imagery, which utilises a satellite-derived normalised difference water index (NDWI) and morphological operators, supraglacial channels and lakes were effectively mapped and quantified across the study region, including meltwater area, meltwater area fraction, channel drainage density (Dd), lake density and comparisons of satellite-derived drainage mapping to regional climate model (MAR) runoff.  </p><p>Results reveal the migratory behaviour of the supraglacial drainage network at Humboldt Glacier as surface runoff increases and the snowline recedes through the melt season. In the high melt years of 2016, 2019 and 2020, Dd commonly peaks in early-July as the ‘inefficient’ system (with hydrologically-connected saturated slush zones) advances inland, before decreasing as the system reaches maximum ‘efficiency’ and inland extent (late-July) before waning as the melt season ends. During these years, this annually-expansive network consistently reaches elevations of ~1450 m (~80km inland), with surface meltwater area covering between 7.2 - 11.6% of the area <1500 m. Retardation to this behaviour is notably observed within the low melt years of 2017 and 2018, when Dd and melt area do not peak until August.</p><p>Supraglacial lakes are also widely present within the drainage system, with their number and size also shown to peak with Dd before decreasing as the melt season progresses, attributed to increased moulin connectivity and subsequent lake drainage events. The combined meltwater area fraction (%) of both supraglacial channels and lakes is strongly correlated with MAR modelled surface runoff.</p><p>This work provides important advancements in the mapping, quantification and understanding of the expansive yet ephemeral supraglacial hydrologic system that exists across northwest Greenland Ice Sheet and its influence on the routing and evacuation of meltwater from these systems and beyond.</p>

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