Catching the fly in dystopian times
Environmental variables determining the distribution of an avian parasite: the case of the Philornis torquans complex (Diptera: Muscidae) in South America
Host-parasite interactions are ubiquitous on Earth. They are present in almost every conceivable ecosystem and often result from a long history of antagonist coevolution [1,2]. Recent studies on climate change have revealed, however, that modification of abiotic variables are often accompanied by shifts in the distributional range of parasites to habitats far beyond their original geographical distribution, creating new interactions in novel habitats with unpredictable consequences for host community structure and organization [3,4]. This situation may be especially critical for endangered host species having small population abundance and restricted distribution range. The infestation of bird species with larvae of the muscid fly genus Philornis is a case in point. At least 250 bird species inhabiting mostly Central and South America are infected by Philornis flies [5,6]. Fly larval development occurs in bird faeces, nesting material, or inside nestlings, affecting the development and nestling survival.
Recent reports indicate significant reduction of bird numbers associated with recent Philornis infection, the most conspicuous being Galapagos finches [7,8]. One way to prevent this potential effect consists in to examine the expected geographical shift of Philornis fly species under future climate change scenarios so that anticipatory conservation practices become implemented for endangered bird species. In this regard, Ecological Niche Modeling (ENM) techniques have been increasingly used as a useful tool to predict disease transmission as well as the species becoming infected under different climate change scenarios [9-11]. The paper of Cuervo et al.  is an important advance in this regard. By identifying for the first time the macro-environmental variables influencing the abiotic niche of species of the Philornis torquans complex in southern South America, the authors perform a geographical projection model that permits identification of the areas susceptible to be colonized by Philornis species in Argentina, Brazil, and Chile, including habitats where the parasitic fly is still largely absent at present. Their results are promissory for conservation studies and contribute to the still underdeveloped issue of the way climate change impacts on antagonistic ecological relationships.
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 Carvalho BM, Rangel EF, Ready PD, Vale MM (2015) Ecological niche modelling predicts southward expansion of Lutzomyia (Nyssomyia) flaviscutellata (Diptera: Psychodidae: Phlebotominae), vector of Leishmania (Leishmania) amazonensis in South America, under climate change. PLOS ONE, 10, e0143282. doi: 10.1371/journal.pone.0143282
 Garrido R, Bacigalupo A, Peña-Gómez F, Bustamante RO, Cattan PE, Gorla DE, Botto-Mahan C (2019) Potential impact of climate change on the geographical distribution of two wild vectors of Chagas disease in Chile: Mepraia spinolai and Mepraia gajardoi. Parasites and Vectors, 12, 478. doi: 10.1186/s13071-019-3744-9
 Cuervo PF, Percara A, Monje L, Beldomenico PM, Quiroga MA (2020) Environmental variables determining the distribution of an avian parasite: the case of the Philornis torquans complex (Diptera: Muscidae) in South America. bioRxiv, 839589, ver. 5 peer-reviewed and recommended by PCI Ecology. doi: 10.1101/839589
Rodrigo Medel (2020) Catching the fly in dystopian times. Peer Community in Ecology, 100049. 10.24072/pci.ecology.100049
Evaluation round #113 Jan 2020
DOI or URL of the preprint: 10.1101/839589
Version of the preprint: 1
Decision by Rodrigo Medel
Dear Dr. Cuervo and Dr. Quiroga,
I received three reviews of your paper entitled "Experimental variables determining the presence of an avian parasite: the case of the Philornis torquans complex (Diptera: Muscidae) in South America". After checking their comments, it is perfectly clear they agree this is an interesting contribution that will make an important contribution to the literature on parasitic flies-bird relationships. However, they also pointed out a number of issues that need to be addressed before accepting your contribution. You can check directly their pdfs for specific recommendations. However, I would like you to consider especially the following observations.
- A clear sentence in the Introduction section that provides a justification to carry out this study is needed. Likewise, a sentence at the end that provides a strong take-home message.
- Consider (if the major aim of this ms basis on conservation) a sentence on how the results of this work may contribute to conservation.
- Consider to include additional information on the host range of P. torquatus (if available).
- Please include information on the extent to which the distribution of host species accounts for the geographic distribution of P. torquans. In the absence of information you can include a sentence discussing this issue.
- Discuss whether environmental factors act directly on P. torquans distribution or indirectly, through bird hosts as host availability may determine parasite distribution by itself.
- Include information regarding the way locations were chosen (random?, from the available literature?). This seems to be a sensitive issue because of a potential spatial autocorrelation of study sites.
- Did you examine the sensitivity of model accuracy to the sample size used?
- Please consider (or explain) the issue that only 3 out of 900 models met the criteria for inclusion. Did you correct for multiple tests?
- Consider to reduce the discussion section (paragraphs 366-389) may be collapsed to make the point more clear.
- Consider including Figs S1 and S2 in the main text. Fig 3c needs a better legend.
- Please include in the Discussion section or supplementary material a list of the potential or current bird species affected by the fly complex.
I look forward receiving you revised manuscript.