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Population Dynamics of Melanorivulus Rossoi, a Restricted Geographic Distribution Killifish Species

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Population Dynamics of Melanorivulus Rossoi, a Restricted Geographic Distribution Killifish Species Environ Biol Fish (2018) 101:245–255 https://doi.org/10.1007/s10641-017-0695-x Population dynamics of Melanorivulus rossoi, a restricted geographic distribution killifish species Francisco Severo-Neto & Matheus Vieira Volcan Received: 15 April 2017 /Accepted: 30 October 2017 /Published online: 9 November 2017 # Springer Science+Business Media B.V., part of Springer Nature 2017 Abstract Species of Melanorivulus present behaviour peaks in September and February. Fire occurred in June, and physiological traits that allow them to live in mar- but no difference in population parameters was observed ginal aquatic habitats. In particular, Melanorivulus after this event. A decrease in the abundance of rossoi is a small nonannual fish only known from its Melanorivulus was related with an increase in the abun- type locality in the Brazilian Cerrado. In this study, we dance of Erythrinidae juveniles. This might be ex- aimed to characterize the distribution and temporal var- plained by an increased predation of this species over iation in body size, sex ratio, density, length-weight the M. rossoi individuals, when the population was relationship (LWR) and condition factor (CF) of reduced to about 30% of that in the previous months. M. rossoi in its natural habitat. To accomplish this, fish We report four new locations where this species was samples were taken monthly for a year using sieve nets recorded; thus, similar to most Rivulidae members, every 30 min. Body size of males and females increased M. rossoi has a restricted distribution area and is threat- throughout the year until early summer. LWR was sig- ened with extinction. Therefore, our results may be nificant, and general coefficient of determination (r2) useful in developing management strategies aimed at was 92%. Juveniles showed negative allometric growth, conservation of this species and its habitat in Brazil. but adults showed positive allometric growth. Both sexes presented the same tendency of temporal variation Keywords Melanorivulus . Wetlands . Rivulidae . in CF, with lower values in October and January and Cerrado . Threatened species F. Severo-Neto (*) Universidade Federal de Mato Grosso do Sul, Cidade Introduction Universitária, CEP 79070-700, Campo Grande, Mato Grosso do Sul, Brazil e-mail: [email protected] Rivulidae is a Neotropical fish family composed of species that inhabit an extensive range of aquatic habi- F. Severo-Neto tats, such as pools, swamps and floodplains (Loureiro Instituto de Biociências, Letras e Ciências Exatas, Departamento and de Sá 2015). Like the African Notobranchiidae, de Zoologia e Botânica, Laboratório de Ictiologia, Universidade Estadual Paulista BJúlio de Mesquita Filho^(UNESP), both included in the suborder Aplocheilodei, some spe- Rua Cristóvão Colombo, 2265, Jardim Nazareth, CEP, cies have the capacity to survive in habitats unsuitable São José do Rio Preto, SP 15054-000, Brazil for other fish, such as intertidal or ephemeral pools (Turko and Wright 2015). Most members of these fam- M . V. Vo lc an Laboratório de Ictiologia, Instituto Pró-Pampa (IPPampa), Rua ilies exhibit egg diapauses, a characteristic that favours Uruguai, 1242, CEP, Pelotas, Rio Grande do Sul 96010-630, embryo survival after dissecation (Furness 2015). Brazil However, in some Rivulidae genera, diapause is 246 Environ Biol Fish (2018) 101:245–255 lacking, and they are considered nonseasonal species Methods (Furness 2015). Some of those species present amphib- ious habits (Turko and Wright 2015) and tolerance to Study area extreme environmental condition, allowing them to live in marginal aquatic habitats, even in low-quality waters The study area is located in the boundaries of Campo unfit for most fish species, e.g., habits with low dis- Grande City, Mato Grosso do Sul, western Brazil. The solved oxygen, low pH and high ammonia concentra- altitude is about 480 m, and the region is located on the tion (Taylor 2012). right bank of the Anhanduí River, Paraná Basin, One nonseasonal rivulid genus, Melanorivulus,was bounding the Paraguay River Basin to the West. recently established by Costa (2011). It was defined on Historically, the area used to be a large connected the basis of species formerly placed in Rivulus.Thisgenus wetland now divided by a state highway and includes about 50 small species (e.g., Loureiro and de Sá surroundedbyfieldsofcornandsoybeancrops 2015; Nielsen et al. 2016;Costa2017;Volcanetal.2017) periodically sprayed with pesticides. The few with most species occupying the Brazilian Cerrado, in marshesthatstillexistarelegalreservesoffarms, particular the upper Paraná Basin which, with its rich fragments of native vegetation that the proprietary drainage, presents a total of 15 Melanorivulus species are required to maintain in accordance with Brazilian (Eschmeyer et al. 2017). In Mato Grosso do Sul State of law. The study area is found within the Cerrado western Brazil, eight Melanorivulus species have thus far ecoregion (Morrone 2014) and follows the Aw classifi- been described, two to the upper Paraguay Basin and six to cation of Koppen-Geiger (Peel et al. 2007 ), with rainy the upper Paraná Basin (Costa 2005;Volcanetal.2017). summers and dry winters. Most of them have a restricted distribution, and some are only known to a single site. Such is the case for Sampling Melanorivulus rossoi (Costa 2005), only known for its type locality, a small tributary from Anhanduí River drain- In order to search for new populations of Melanorivulus age, which flows from the right margin of the Paraná rossoi, satellite images from Google Earth (earth.google. River. com) were analyzed to identify potential sites for species Most species of the Rivulidae family are threatened occurrence. Fieldwork was carried out by traveling the with extinction, and little is known about their distribu- highways and secondary unpaved roads to access tion area and ecology (Rosa and Lima 2008; Volcan potential sites. An active search for fish was performed et al. 2017). Similarly, the occurrence area of M. rossoi by two researchers using sieves 45 cm in diameter with is threatened by landscape modification for agricultural 5 mm mesh at every site recorded. When we identified use, and basic biological information about the species even a single individual, we took it to indicate the presence is still unknown. The population dynamics and life of the species in the marsh, but not necessarily history of these highly endemic species, as well as their homeogeneous occupation. density responses to seasonal and weather changes, such Since access to private land was limited, we as pluviosity and temperature, can be understood chose a single wetland (20°37′44″S, 54°45′04″ through long-term monitoring (Douglas and Marsh W, Fig. 1) for the monthly monitoring of popula- 1996; Ebner and Thiem 2009; Van Haverbeke et al. tion dynamics. The marsh comprises an area of 2013). However, most studies with this approach focus 53 ha, average depth of 40 cm and vegetal cover- on species related to fisheries, and little attention has age of Poaceae. been given to the smallest species. The samples were taken monthly from April 2015 to Therefore, in the present study, we aimed to verify the March 2016 using the method noted above during distribution and temporal variationinbodysize,sexratio, 30 min. To avoid bias from monthly removal of indi- density, length-weight relationships (LWR) and condition viduals from the site, the specimens were anesthetized factor (CF) of M. rossoi in its natural habitat. Interestingly, with eugenol at 0.1 mg/L. Afterwards, specimens were during the course of this study, two unpredicted variables counted, sexed, and total (TL) and standard length (SL) emerged: fire in the marsh during the dry season and an were measured with a digital caliper. Between April and explosive abundance of Erytrhinidae juveniles, which are August, the first 60 individuals sampled were weighed putative predators of M. rossoi. on a 0.001 precision digital scale, kept in plastic Environ Biol Fish (2018) 101:245–255 247 Fig. 1 Map with the distribution of Melanorivulus rossoi populations. Star represents the species type locality, and the red circle indicates the marsh where the monthly collections took place receptacles to avoid resampling, and returned to the In order to identify which species consume M. rossoi environment after recovering from the effects of euge- individuals, the identified putative predators [Hoplias nol. In the following months, all collected individ- malabaricus (Bloch, 1794), Hoplerythrinus unitaeniatus uals were measured and weighed since abundance (Spix & Agassiz, 1829), Synbranchus marmoratus (Bloch, was low. Species was confirmed through the orig- 1795), and Gymnotus spp.] were fixed on formalin solu- inal description by Costa (2005). Since the original tion 10% and later transferred to alcohol 70%. In the description does not include differences between laboratory, their gastric contents were analysed under sexes, females were determined through general stereomicroscopy. All collections were authorized by the phenotypic criteria on Melanorivulus species (Huber 1992), which indicate that the female pre- sents a conspicuous ocellus near the top origin of the caudal fin, and this was confirmed later with gonadal analysis of the specimens. More specifi- cally, M. rossoi females present a distinct ocellus, brownish dots below the middle of the flank, black spots/stripes on the caudal fin, and absence of red dots on the dorsal fin (Fig. 2). Individuals that could not be differentiated externally were consid- ered juveniles. Occurrence and abundance of non- Rivulidae fish species of the marsh were recorded monthly, and identification was performed with reference to Britski et al. (2007) and Graça and Pavanelli (2007), in addition to direct analysis of specimens from the Coleção Zoológica da Universidade Federal de Mato Fig. 2 Melanorivulus rossoi male above and female below. Non- Grosso do Sul (ZUFMS). preserved individuals 248 Environ Biol Fish (2018) 101:245–255 responsible environmental agency (ICMBio, under license Results N°49,242). Voucher specimens were deposited in ZUFMS. Distribution of Melanorivulus rossoi was extended to four other sites (Fig.
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