Native macrophyte leaves influence more specialisation of neotropical shredder chironomids than invasive macrophyte leaves

Abstract

We investigated the composition and specialisation of shredder chironomids in an invasive white ginger lily (Hedychium coronarium) and in native pickerelweed (Pontederia cordata) leaves. We assumed that the difference of the chemical compound in macrophyte leaves would influence the shredder specialisation. A colonisation experiment was performed over 3 years (2013–2015) using 40 bags for each macrophyte species. The main macrophyte leaf chemical compounds (organic matter, nitrogen, phosphorus, cellulose, lignin, soluble polyphenols and soluble carbohydrates) were measured. The herbivore specialisation was estimated using the individual specialisation index (d′) and community specialisation index (H2′). White ginger lily had higher nitrogen and organic matter, resulting in a higher abundance of shredder specimens and lower specialisation than in native leaves. The Polypedilum fallax group, Stenochironomus and Endotribelos calophylli presented high individual specialisation (d′) in pickerelweed leaves, resulting in high community specialisation (H2′). The heterotrophic facilitation hypothesis explained the herbivores thriving in pickerelweed leaves due to their lower nutritional value. The intake-efficiency hypothesis explained the higher consumption of invasive plant tissue by Stenochironomus, due to its mining habit. We found evidence of evolutionary adaptation of freshwater herbivore eating habits.