Foraging preferences of Barn swallow (Hirundo rustica) analysed by metabarcoding along an urban-rural gradient in Japan

Abstract

In the current context of urban expansion, natural environments face many changes. Loss of biodiversity, species adaptation, trophic relationships modifications and many other alterations result from this phenomenon and raise conservation concerns. Understanding the interactions between urban environments and organisms is critical in order to tackle the urbanization-related conservation problematics and to take relevant actions to mitigate the disturbances generated by the urban sprawl. This master thesis aims at investigation the relationship between an Urban-Rural gradient and variables commonly linked to the urbanization phenomenon with the foraging preferences of Hirundo rustica (Linnaeus, 1758). This bird, well present in cities and appreciated for feeding on pest species display differences in morphological and breeding characteristics in urbanized areas. This work strives to measure the impact of this urban sprawl on the foraging behavior and to contribute to the diet studies realized via the DNA metabarcoding technique. In order to achieve these goals, Hirundo rustica (Linnaeus, 1758) feces were collected in 75 sampling sites in the Kanto region, Japan. The data collection took place in June and July 2020. The DNA sequences from the COI-5P region present in the excrements were sequenced via the DNA metabarcoding technique and a taxonomy was assigned to these DNA fragments thanks to a Basic Local Alignment Search Tool (BLAST) on a complete reference sequence database from the National Center for Biotechnology Information and on a curated Barcode of Life Data System database limited to the Japanese insects’ records. The results obtained through both databases were compared. Three times less species were identified with the curated database, and it was suggested that this specific database needed more contribution and development to accurately investigate insectivorous organisms’ diet. These analyses imply that Hirundo rustica (Linnaeus, 1758) mostly feeds on Diptera. Coleoptera, Lepidoptera, Hemiptera and Hymenoptera represent an important part of its diet as well. The α diversity of insects found in the fecal matter was then assessed for each sampling site. The Shannon and the observed taxa richness were calculated in this purpose. The β diversity between sampling sites was estimated as well via the Jaccard index. The relationship with the urban-rural gradient and the environmental variables has been studied with Generalized Linear Mixed Models for the α diversity and with a Permutational Multivariate Analysis of Variance for the β diversity.

The obtained results suggest that the fragmentation, the average temperature, the amount of precipitation and the radiance explain variation in the α diversity. As for the β diversity, significant statistical relationships with the average temperature, the range of temperatures and the amount of precipitation have been found.

This study attempts to provide relevant information to the scientific communities and to help understanding how trophic interactions change with disturbances generated by urbanization, providing support in decision-making process for the establishment of green infrastructures and the implementation of environmental measures in territories affected by the urban sprawl.