Use the following type of citation: North-western Journal of Zoology 2021: e211509 1 *Handling editor: Yurii Kornilev 2 *Manuscript Domain: Herpetology of the Americas 3 *Manuscript code: NwJZ_20_HA_13 4 *Submission date: 11_06_2020 5 *Revised: 17_03_2021 6 *Accepted: 24_03_2021 7 *No. of words (without abstract, acknowledgement, references, tables, captions): 4830 8 *Editors only: 9 10 Title of the paper: Diet variation of the South American snake-neckedZoology turtle of 11 (Hydromedusa tectifera) from two different urban neighboring streams 12 Running head: Diet of Hydromedusa tectifera in urban streams paper 13 Authors: Rocío María Sánchez, María BelénJournal Semeñiuk, María Julia Cassano, Leandro 14 Alcalde 15 Key Words: Argentine snake-neckedaccepted turtle, diet composition, prey selection, urban 16 environment, feces, stomach flushing 17 North-Western 18 No. of Tables: 2 19 No. of Figures: 4 20 No. of Files: 36 21 22 23 1 Use the following type of citation: North-western Journal of Zoology 2021: e211509 24 Diet variation of the South American snake-necked turtle (Hydromedusa tectifera) 25 from two different urban neighboring streams 26 27 Rocío María SÁNCHEZ *, María Belén SEMEÑIUK, María Julia CASSANO and Leandro 28 ALCALDE 29 30 Sección Herpetología, Instituto de Limnología Dr. R. A. Ringuelet (CONICET- 31 UNLP). Boulevard 120 y 62 n° 1437, CP 1900, La Plata, Buenos 32 Aires, Argentina 33 Zoology of 34 * Corresponding author, R. M. Sánchez, E-mail: [email protected] 35 paper 36 Abstract. Dietary studies provide data aboutJournal the biology of species such as food 37 specialization, spatial and temporal feeding variation and adaptations to different habitat 38 characteristics. We analyzed the diet acceptedof the South American snake-necked turtle 39 Hydromedusa tectifera using complementary techniques (stomach flushing and feces 40 collection) from twNorth-Westerno urban watercourses in La Plata city (Buenos Aires, Argentina), one 41 more natural and other more polluted. The Index of Relative Importance (IRI) was 42 calculated to assess the contribution of each prey to the diet, and the Index of Electivity (E) 43 to evaluate food selection. In general, H. tectifera displayed a generalist carnivorous habit 44 with clear adaptations to variations in the environments in which this species lives. The diet 45 composition showed marked differences between the two streams: in the more impacted 46 watercourse, amphipods, aquatic coleopterans and water bugs of the family Belostomatidae 47 were the main items, while in the less anthropogenically disturbed one, aquatic snails 2 Use the following type of citation: North-western Journal of Zoology 2021: e211509 48 dominated the turtles’ diet. Our results highlight the importance of combining stomach 49 flushing and fecal collection techniques to achieve a better trophic characterization and to 50 avoid biased conclusions. 51 52 Key words: Argentine snake-necked turtle, diet composition, prey selection, urban 53 environment, feces, stomach flushing. 54 55 Running title: Diet of Hydromedusa tectifera in urban streams 56 57 Introduction Zoology of 58 Dietary studies supply important data on the biology, physiology and natural history of a 59 species, as well as information regarding local restrictions such as prey availability or intra- paper 60 and inter- specific interactions (Ottonello etJournal al. 2017). Moreover, knowledge about what an 61 animal eats and what its feeding preferences are is a useful tool for environmental 62 management and conservation programs.accepted 63 Globally, most lotic and lentic ecosystems have been highly affected by urbanization, since 64 they were usually North-Westernchosen for human settlements (Bodie 2001). In this context, 65 understanding how habitat transformations shape the ecological niche dimension of species 66 becomes crucial to mitigate impacts, promote restoration actions and generate long-term 67 conservation programs on freshwater ecosystems (Bodie 2001, Spinks et al. 2003). 68 Feeding habits of urban freshwater turtle populations have been assessed for several species 69 around the world (Souza & Abe 2000, Wilson & Lawler 2008, Wilhelm & Plummer 2012, 70 Stephens & Ryan 2019). In some cases (e.g., Phrynops geoffroanus), variations in feeding 3 Use the following type of citation: North-western Journal of Zoology 2021: e211509 71 habits between individuals from urban and non-urban sites have been reported (Ferronato et 72 al. 2013). 73 The exclusively aquatic medium size South American snake-necked turtle Hydromedusa 74 tectifera Cope, 1870 is distributed from southern Brazil and southeastern Paraguay to 75 northeastern and central Argentina and almost all of Uruguay (Sánchez et al. 2019). It 76 inhabits highly diverse environments like ponds, lagoons, rivers, and streams. Some of 77 these habitats are located in urban areas affected by different sources of pollution such as 78 industrial discharges, sewage and toxins from farming activity. Previous work on the diet of 79 H. tectifera demonstrated that this species is generalist, zoophagous and preys on a wide 80 variety of invertebrates and vertebrates, mainly aquatic arthropods,Zoology mollusks , fish and even of 81 carrion (Bonino et al. 2009, Alcalde et al. 2010). It has probably a reduced home-range 82 evidenced by the high number of recaptures obtained in one or two period studies (Lescano paper 83 et al. 2008, Semeñiuk et al. 2019). Journal 84 The present study compares diet composition and prey selection of H. tectifera in two 85 neighboring urban streams with contrastingaccepted habitat character istics. The research was 86 designed to test the hypothesis that feeding habits of turtles from both streams reflect the 87 differences observedNorth-Western in the environmental characteristics of their respective habitats. We 88 expected that a more diverse diet would be observed in the less anthropogenically modified 89 stream than in the more impacted stream. 90 Materials and methods 91 Field work was carried out in two urban streams, Rodríguez and Carnaval (La Plata city, in 92 northeastern Buenos Aires province, Argentina; Fig. 1) The study area was located in the 93 southern limit of the AMBA (Area Metropolitana de Buenos Aires), the most populated 4 Use the following type of citation: North-western Journal of Zoology 2021: e211509 94 region of the country, with a population of about 14 million people (37% of the Argentinian 95 population) and a density of 1140 people/km2 (INDEC, 2010). 96 Both streams are tributaries of the Río de la Plata River and part of the southernmost core 97 of the distribution of H. tectifera (Sánchez et al. 2019). These Pampean streams share 98 characteristics typical of most of the watercourses of the region: high turbidity, low basin 99 slope and low-water depths periodically interrupted by flooding due to heavy rains. 100 Both streams receive untreated domestic water discharges and solid garbage (e.g. bottles, 101 plastics, food remains) from the neighboring houses in the section they cross the city. 102 Overall, the housing density was higher around Rodríguez than in Carnaval (Fig.1). The 103 Rodríguez stream also receives industrial effluents without appropriZoologyate treatment (a meat of 104 processing plant and a pork farm) and untreated sewage from the Grand Bell neighborhood. 105 Due to the high density of housing and the above-mentioned water discharges, Rodríguez paper 106 has a permanent flow of water even duringJournal drought periods (summer). On the contrary, the 107 headwaters and part of the middle section of Carnaval can dry up since its flow depends 108 mainly on underground water which isaccepted sometimes overexploited (Rodrigues Capítulo L. et 109 al. 2020). 110 Previous investigationsNorth-Western of the two streams revealed poorer water quality in Rodríguez, 111 evidenced by high values of conductivity, organic matter, nutrients and oxygen chemical 112 demand, as well as low values of dissolved oxygen (López van Oosterom et al. 2015, 113 Lavarías et al. 2017). Furthermore, the contamination with organic matter of Rodríguez was 114 also evidenced by alterations of biological functions in hemipterans (Lavarías et al. 2017) 115 and the presence of annelid families associated with organic pollution (López van 116 Oosterom et al. 2015). Based on biotic indices of macroinvertebrate assemblages Rodríguez 117 was classified as heavily polluted (Bauer et al. 2002, Lopez van Oosterom et al. 2014) and 5 Use the following type of citation: North-western Journal of Zoology 2021: e211509 118 Carnaval as slightly/moderately polluted (Lopez van Oosterom et al. 2014, Rodrigues 119 Capítulo A. et al. 2020). 120 Another important difference between the streams is that Carnaval had markedly higher 121 abundance and diversity of aquatic macrophytes compared to Rodríguez. Indeed, we 122 identified 16 species and two genera of aquatic macrophytes for Carnaval, classified as 123 submerged (s), floating-leaved (f) or emergent (e): Egeria densa, Elodea callitrichoides, 124 Stuckenia striata (s); Alternanthera philoxeroides, Hydrocleys nymphoides, Hydrocotyle 125 ranunculoides, Lilaeopsis spp., Ludwigia peploides, Nasturtium officinale, Polygonum 126 punctatum (f); Cyperus eragrostis, Eleocharis elegans, Iris pseudacorus, Ludwigia elegans, 127 Sagittaria montevidensis, Schoenoplectus spp., SchoenoplectusZoology californicus , and Senecio of 128 bonariensis (e). In contrast, only five of these aquatic plant species were found in the 129 sampled