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Table 1 Overview of 31 studies to date examining the ecology, behavior and genetics of the Darwin’s finch Philornis downsi host-parasite system since the first discovery of P. downsi larvae in Darwin’s finch nests on Santa Cruz Island, Galápagos Archipelago, in 1997. Shown are data for 1) Number of finch host species or species name when singular, 2) Island, 3) Year study undertaken, 4) Sample size of nests (including number of control versus experimental [Exp.] nests), 5) P. downsi prevalence, 6) Mean number and range of P. downsi (in unmanipulated nests), 7) Percentage of in-nest mortality of nestlings in unmanipulated nests, 8) Effects on host, 9) Additional comments, 10) Type of study (Ecology, Genetics, Behavior), 11) Experimental study (E) versus Observational study (O), 12) Reference

From: Host-parasite ecology, behavior and genetics: a review of the introduced fly parasite Philornis downsi and its Darwin’s finch hosts

1) Host species 2) Island 3) Year of study 4) Sample size 5) P. downsi prevalence 6) Mean number of P. downsi per nest (range) 7) In-nest mortality (%) 8) Effects on host 9) Comments 10) Type of Study 11) Exp. (E) versus Obs. (O) study 12) Reference
9 species Santa Cruz 1998 63 97 %    N/A First study to describe P. downsi in bird nests on Santa Cruz Island Ecology O Fessl, Couri, Tebbich 2001 [29]
12 species Santa Cruz 1998–2000 177 97 % 15.7 ± 7.4–49.8 ± 31.2 (0–182) 27 % Number of larvae increased with nestling age; P. downsi not found in nests during incubation Intensity compared for nestling age <8 days vs. >8d; species differed in intensity Ecology O Fessl, Tebbich 2002 [28]
3 Darwin’s finch species Santa Cruz 2000, 2004, 2005 63 100 %   −32.4–95.2 % Damage to nestling nasal cavities; calculated 18–55 % overnight blood loss in nestlings due to parasitism Identify two stage life cycle of P. downsi with 1st instar within nestling nares and 2nd and 3rd instar feeding externally Ecology O Fessl, Sinclair, Kleindorfer 2006 [42]
2 Darwin’s finch species Santa Cruz 2000, 2004 27 100 % 18.4 ± 2.4–23.2 ± 4.2 66 % Parasitized nestlings had 61 % lower survival, 56 % lower body mass, 28 % lower hemoglobin concentration 11 nests prayed with 1 % permethrim (~1 P. downsi left per nest; range 0–5 larvae) Ecology E Fessl, Kleindorfer, Tebbich 2006 [41]
Darwin’s finches All islands       P. downsi given highest risk ranking for invasive species that negatively impact endemic fauna 23 % (around 463 species) of Galapagos invertebrate species are introduced of which 6 are confirmed to be highly invasive and harmful to endemic species Ecology   Causton, Peck, Sinclair, Roque-Albelo, Hodgson, Landry 2006 [26]
Small ground finch Santa Cruz, Floreana, Isabela 2004 24 92 % 23 ± 6 (0–90)   2 % lower hemoglobin concentration per additional larva Effect of clutch size on P. downsi number per nestling Ecology O Dudaniec, Kleindorfer, Fessl 2006 [44]
6 Darwin’s finch species Santa Cruz 1998–2005 131 100 % 30.2 ± 4–66.8 ± 7.6 55 % Positive association between P. downsi intensity and rainfall (eight year study); same intensity across habitats on Santa Cruz Species differences in intensity Ecology O Dudaniec, Fessl, Kleindorfer 2007 [33]
Darwin’s finches 13 islands 1998–2005 515   27.0 (1–182)   P. downsi was found on 11 of 13 islands sampled (absent from flat arid islands); more parasites in highland nests on elevated islands Lowland nests on elevated islands had more P. downsi than lowland nests on flat islands Ecology O Wiedenfeld, Jiménez, Fessl, Kleindorfer, Valarezo 2007 [39]
5 Darwin’s finch species Santa Cruz, Floreana, Isabela 2004–2006 64 100 %    High gene flow between islands; some genetic differentiation of P. downsi on Floreana; evidence for genetic bottleneck Sequenced CO1 mitochondrial gene fragments Genetics, Ecology O Dudaniec, Gardner, Donnellan, Kleindorfer 2008 [40]
Medium ground finch Santa Cruz 2004–2006 63 64–98 % (0–200) 16–37 % Number of P. downsi per nestling (but not per nest) predicted survival; no effect of P. downsi on nestling size Nests earlier in the breeding season had more P. downsi per nest Ecology O Huber 2008 [34]
Small ground finch Santa Cruz 2008 623     36.3 % of adult birds had malformed beaks with enlarged naris (likely caused by P. downsi during the nestling phase)   Ecology O Galligan, Kleindorfer 2009 [48]
5 Darwin’s finch species Santa Cruz 2000–2004 43 100 % 23.0 ± 3–57.0 ± 4   Larger finches built larger nests; within species, larger nests had more P. downsi   Behavior O Kleindorfer, Dudaniec 2009 [90]
Small ground finch Floreana 2004–2006 39 94 % 8.0 ± 1.6–39.3 ± 4.6 (0–78) 3–33.4 % Arid lowland nests had 80 % fewer P. downsi and 91 % lower in-nest mortality than highland nests   Ecology O O’Connor, Dudaniec, Kleindorfer 2010 [89]
Medium ground finch Santa Cruz, Daphne Major 2008 67     More Philornis-specific antibodies in females than males, and more during the nesting period No P. downsi found on Daphne Major Ecology, Behavior O Huber, Owen, Koop, King, Grant, Grant, Clayton 2010 [46]
3 Darwin’s finch species Santa Cruz, Floreana 2008 11 89 % 27.1 ± 8.5 (0–74) 79.2 % Multiple P. downsi entries into the nest during incubation and feeding; nestlings stood on top of each other presumably to avoid larvae; adults preened nestling nares and nest base; nestling consumed larva In-nest video; altered time budgets and behavior in heavily parasitized nests; adults removed dead nestling from nest Behavior, Ecology O O’Connor, Robertson, Kleindorfer 2010 [49]
5 Darwin’s finch species Santa Cruz, Floreana 2004–2006 57 100 % 30.8 ± 16.5 (5–65)   Genetic relatedness among P. downsi within nests was 57 % lower on Santa Cruz than on Floreana Island; between 1–6 different females laid their eggs per finch nest; each female mated with ~2 different males; each female laid ~5 eggs per finch nest with a maximum of 24 from one female   Genetics, Ecology, Behavior O Dudaniec, Gardner, Kleindorfer 2010 [117]
Medium tree finch Floreana 2006, 2008 30 100 % 43.1 ± 10.7–65.6 ± 8.5 (8–96) 20–38 % total brood loss; 53 % of nests with partial or total brood loss Parasite intensity did not predict fledging success; parasitized nestlings had grossly enlarged nares and tissue loss Highest P. downsi intensity in critically endangered medium tree finch Ecology O O’Connor, Sulloway, Robertson, Kleindorfer 2010 [38]
Mangrove finch Isabela 2006–2009 15 100 40.8 ± 15.3 sd 14 % Less rat predation after rat control (30 % predation after control versus 54 % predation before); P. downsi explained 14 % nestling mortality Before and after rat control Ecology O + E Fessl, Young, Young, Rodríguez-Matamoros, Dvorak, Tebbich 2010 [63]
Medium ground finch Santa Cruz 2008 48 90 % 37.5 ± 4.9 96 % Parasitized nestlings had ~30 % shorter primary feather length and 88 % lower fledging success Nylon stocking placed over wire hoop as barrier to P. downsi; reduced parasite intensity to ~21 larvae per nest Ecology, Behavior E Koop, Huber, Laverty, Clayton 2011 [63]
Darwin’s finches All islands 2012-present      Summary of known P. downsi biology and impacts on endemic land birds Launch of the P. downsi Action Plan Ecology, Behavior, Genetics   Causton, Cunninghame, Tapia 2013 [72]
Medium ground finch Santa Cruz 2010 30 (15 control, 15 exp.)   44.7 ± 6 (5–79)   No effect of P. downsi on attending female corticosterone level, body condition or hematocrit level 15 nests sprayed with 1 % permethrin (~0 per nest)   E Knutie, Koop, French, Clayton 2013 [102]
Medium ground finch Santa Cruz 2010 43 (22 control,21 exp) 100 % 38.5 ± 5.1 100 % Compared with fumigated nests, females at parasitized nests had more P. downsi-specific antibodies, spent 42 % less time brooding and 74 % more time standing erect in the nest 14 females and 10 males from fumigated nests, 15 females and 10 males from parasitized nests Behavior E Koop, Owen, Knutie, Aguilar, Clayton 2013 [47]
Medium ground finch Santa Cruz 2009 13 (7 control, 6 exp.) 83 % 30.5 ± 7.5 86 % No effect of rainfall on P. downsi intensity (two year study) 6 nests sprayed with 1 % permethrin (zero P. downsi) Ecology E Koop, Le Bohec, Clayton 2013 [88]
Small ground finch Floreana 2010 14 (7 control, 7 exp.) 100 % 22.7 ± 3.9 (12–60) 100 % In-nest video; heavily parasitized nestlings had weak begging; parents only fed strongly begging nestlings 7 nests sprayed with 1 % permethrin (zero P. downsi) Behavior E O’Connor, Robertson, Kleindorfer 2014 [100]
4 Darwin’s finch species Floreana 2004–2013 238 100 % 27.5 ± 4.6 (2004) to 48.4 ± 6.5 (2013) 50–90 % Across the decade, P. downsi intensity increased (~28 to ~48), in-nest mortality increased (~50 to ~90 %), nestlings died younger (~11 to ~5 days after hatching); pupa size got 10 % smaller (~10 mm to ~9 mm) Compared with other finches, small ground finch nests had more P. downsi pupae, which indicates higher fly reproductive success Ecology O Kleindorfer, Peters, Custance, Dudaniec, O’Connor 2014 [37]
3 Darwin’s tree finch species Floreana 2005, 2010 201 100 % 25 ± 3–65 ± 18   Hybrid finch nests had 50–79 % fewer P. downsi than medium tree finch (2005, 2010) Contemporary hybridization in Darwin’s tree Finches; evidence for hybrid fitness Behavior, Genetics, Ecology O Kleindorfer, O’Connor, Dudaniec, Myers, Robertson, Sulloway 2014 [7]
2 Darwin’s finch species Santa Cruz 2010, 2012 82 100 % 25, 38 37–56 % Extreme weather events and number of P. downsi influenced nesting success Species differences in P. downsi intensity Ecology O Cimadom, Ulloa, Meidl, Zöttl, Zöttl, Fessl, Nemeth, Dvorak, Cunninghame, Tebbich 2014 [36]
4 Darwin’s finch species Santa Cruz 2013 37 (17 control, 20 exp.) plus 26 nests checked for treated cotton   17 ± 3.9 46 % Parasitized nests had 35 % lower fledging success Permethrin-treated cotton from dispensers in 22 nests; 20 nests sprayed with 1 % permethrin (zero P. downsi) Ecology E Knutie, McNew, Bartlow, Vargas, Clayton 2014 [70]
Small ground finch Floreana 2010 14 (8 control, 6 exp.) 100 % 24.2 ± 2.7   Parasitized nestlings had larger relative (39 %) and absolute (3.3 mm) naris size compared with parasite-free nestlings (20.2 %, 1.6 mm) 6 nests sprayed with 1 % permethrin (zero P. downsi); museum specimens had normal naris size suggesting post 1960s arrival of P. downsi Ecology, Morphology E Kleindorfer, Sulloway 2016 [30]
3 Darwin’s finch species Floreana 2004–2014 582 100 % 17.7 ± 3.3–87.8 ± 19.5   Higher fly traps caught more female P. downsi; higher finch nests had more P. downsi 28 McPhail traps placed at 1 m–7 m to test for fly sex ratio at different trapping heights Behavior, Ecology E Kleindorfer, Peters, Hohl, Sulloway 2016 [71]
Medium ground finch, mockingbird Santa Cruz 2012, 2013 127     P. downsi density (grams per nestling g) predicted finch but not mockingbird mortality; no P. downsi antibodies in nestlings; parasitized mockingbird but not finch nestlings begged more 32 finch nests and 34 mockingbird nests prayed with 1 % permethrin Behavior, Ecology E Knutie, Owen, McNew, Bartlow, Arriero, Herman, DiBlasi, Thompson, Koop, Clayton 2016 [105]