Contributions to Zoology, 82 (1) – 2013Andrea Grill; Andrea Cerny; Konrad Fiedler: Hot summers, long life: egg laying strategies of Maniola butterflies are affected by geographic provenance rather than adult diet

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The Meadow Brown butterfly, Maniola jurtina L., is a widespread western Palaearctic butterfly that lays its eggs on various grass species (Brakefield, 1982a, b; Ebert und Rennwald, 1991, Schweizerischer Bund für Naturschutz, 1987). Adults are strictly univoltine and are on the wing from late May to early October, depending on altitude and climate. As typical for univoltine species (Danks, 2006; Košťál, 2006), this butterfly is adapted to the environmental conditions of its habitat to optimally use seasonally limited resources, in particular larval host plants. As a consequence, it exhibits large ecological plasticity with respect to oviposition strategies. In dry and hot conditions with no grass available for caterpillars to feed on during the summer months, females perform a summer dormancy (aestivation) accompanied by delayed ovarian maturation (Masetti and Scali, 1972). This means that eggs may be kept in the abdomen up to several months after mating and are deposited only in late summer or early autumn, when first rainfall allows for re-growth of grass. It also means that these females are relatively long-lived. For such long-lived butterflies adult diet is of particular importance.

Adult diet can extend lifespan and enhance fertility, as has been shown for example in tropical Bicyclus species (Brakefield and Kesbeke, 1995) and Charaxes fulvescens Aurivillius, 1891 (Molleman et al., 2008). These feed on rotting fruits and hereby enrich their diets with amino acids. Temperate-zone butterflies, like Maniola jurtina, usually rely on floral nectar containing mostly sugars.

The role of carbohydrates in butterfly nutrition is fairly well understood (Bauerfeind et al., 2007 and references therein). Nectar-derived sugars obviously fuel the animals for flight and can also be incorporated into the eggs (Moore and Singer, 1987; Watanabe, 1992; Boggs, 1997; Fischer and Fiedler, 2001), but the role of other substances in adult butterfly nutrition is still a matter of controversy.

Nitrogen is a limiting factor for many herbivorous insects, in particular butterflies (Morehouse and Rutowski, 2010 and references therein; Pellissier et al., 2012). The reason for this are the discrepancies between the structural compounds used by plants to provide support for their tissues (carbon-based polysaccharides such as cellulose and lignin) and the protein complexes needed by insects to construct their bodies (Fagan et al., 2002). As nectar contains little nitrogen (Baker and Baker, 1973, 1975), adults largely depend on larval resources for investment in reproduction, which leads to a depletion of nitrogen stocks during reproduction (Takeuchi, 2012). Additional amino acid content in adult food resources may compensate for this nitrogen loss and lead to greater longevity and larger quantity of eggs. That this can be the case, has been beautifully shown in an experiment with the Map Butterfly, Araschnia levana L. (Mevi-Schütz and Erhardt, 2005), where additional amino acids in the nectar increased the number of eggs laid. Similarly, Boggs (1986, 1997) pointed to the importance of adult nutrition for the reproductive potential, and Geister et al. (2008) have demonstrated that fecundity (measured as the number of eggs laid per lifetime) of tropical Bicyclus anynana (Butler, 1879) was higher when the individuals were fed banana fruits, containing amino acids, than when fed plain sucrose solution. In many cases, however, nitrogen income during the adult stage had no effect on fecundity (Fischer et al., 2004; Moore and Singer, 1987; Hill and Pierce, 1989; Mevi-Schütz and Erhardt, 2003).

Here, we investigated if food resources available to adult Maniola butterflies affect fecundity (i.e. lifetime quantity of eggs), longevity and egg-laying behaviour. Particularly for females which undergo summer dormancy and consequently live about three times as long as their conspecifics from cooler climates, adult nutrition ought to be crucial for the reproductive success and additional amino acid intake should supposedly have beneficial effects on fecundity and lifespan.

To test this, we compared M. jurtina butterflies from populations with expected summer-dormancy with populations without summer-dormancy, including a population of the Sardinian endemic M. nurag, and tested experimentally if increased intake of amino acids could alter (a) timing of oviposition (i.e. days from capture to oviposition), (b) fecundity (i.e. total number of eggs laid), (c) lifespan of adult females, (d) the length of the reproductive period (i.e. number of days while eggs were deposited), or (e) post reproductive lifespan.