Phoretic association between larvae of Rheotanytarsus ( Diptera : Chironomidae ) and genera of Odonata in a first-order stream in an area of Atlantic Forest in southeastern Brazil

In this note, the occurrence of phoresy between larvae of Rheotanitarsus sp. (Diptera: Chironomidae) and larvae of Heteragrion sp. (Odonata: Megapodagrionidae) and of unidentified genera of Calopterygidae (Odonata) collected in a first-order stream in an area of Atlantic Forest in southeastern Brazil is reported. During the dry season of 2007 and the rainy season of 2008, with the aid of a Surber sampler, 15 samples of each of the following mesohabitats were collected: litter from riffle areas, litter from pool areas and sediment in pool areas. Eighty-five Odonata larvae were obtained, 10 (11.76%) with cases of phoresy by Rheotanytarsus sp.. These chironomids were associated with only one specimen of Megapodagrionidae, whereas the other larvae were recorded in association with Calopterygidae. Most of the Odonata with cases of phoresy by Rheotanytarsus sp. were recorded in the dry season. In the present study, the absence of the phoretic association with other potential hosts for Rheotanytarsus sp. found in the samples indicates a possible preference of these larvae for Odonata, which accounted for only 2.42% of the collected macroinvertebrates in litter and sediment.

Phoresy, a relationship in which an organism lives on the body of another organism and is thus carried (TOKESHI 1993), occurs among various organisms from aquatic environments.It has been described as a commensal interaction for several invertebrate taxa, especially chironomid insects, which is the group with the greatest number of records of phoretic association with different genera and species of invertebrates (SEGURA et al. 2007).The commensal hosts for this family are mostly members of the Plecoptera (EPLER 1986), Ephemeroptera (CAL- LISTO & GOULART 2000), Megaloptera (PENNUTO 2003), Odonata (FERREIRA-PERUQUETTI &TRIVINHO-STRIXINO 2003), andTrichoptera (ROQUE et al. 2004).
Most works on chironomid larvae in phoretic association with other organisms are concentrated in North America and Europe (TOKESHI 1993).In Brazil, this relation was previously recorded in lotic environments from the states of São Paulo (FERREIRA-PERUQUETTI & TRIVINHO-STRIXINO 2003), Rio de Janeiro (DORVILLÉ et al. 2000), Mato Grosso do Sul (ROQUE et al. 2004), andMinas Gerais (CALLISTO et al. 2006).The present study records the occurrence of phoresy between larvae of Rheotanytarsus Thienemann & Bause, 1913 (Chironomidae) and larvae of Odonata (Calopterygidae and Megapodagrionidae) in a first-order stream in an area of Atlantic Forest in southeastern Brazil.
The stream is located in a secondary forest, which comprises an area of biological conservation called Reserva Biológica Municipal Poço D'Anta (21°45'S, 43°20'W; altitude varying from 800 to 1040 m).This reserve is located in the municipality of Juiz de Fora, state of Minas Gerais, Brazil.The stream is a shallow environment (5.63 ± 1.43 cm), whose bed is mostly constituted of sand and patches of substrate of stones and leaf litter.The water is transparent and well oxygenated (10.03 ± 0.42 mg/l), with electric conductivity and pH varying around 17.75 ± 2.06 µS/cm and 6.38 ± 0.41, respectively.
During the dry season of 2007 (July to September) and the rainy season of 2008 (January to March), 15 samples of each of the following mesohabitats were collected with the aid of a Surber sampler (250 µm mesh): litter from riffle areas, litter from pool areas and sediment from pool areas.In each month, patches from the four mesohabitats, located in a stretch of 300 m of the stream, were individually sampled during 30 seconds.The samples were fixed in formaldehyde solution 4%,

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Phoretic association between larvae of Rheotanytarsus (Diptera: Chironomidae) and genera of Odonata in a first-order stream in an area of Atlantic Forest in southeastern Brazil Beatriz F. J. Vescovi Rosa In order to verify if there was a significant difference among the number of larvae collected with or without larval cases in the two sample seasons, the Mann-Whitney test was performed.This statistical test was also used in order to verify if there was a significant difference of the mean velocity of the water and the outflow between the dry and the rainy season.The computer program Past, version 1.49 (HAMMER et al. 2001), was employed for performing the statistical tests.
Most of the larval cases (83.33%) were attached on the sternal portion of the Odonata specimens, with the head capsule pointing to the posterior portion of the host's body (Figs 1  and 2).Only two hosts presented more than one case of phoresy by Rheotanytarsus sp.: in Heteragrion sp.one larval case with larvae and another without larvae were found, both on the sternum, while in one individual of Calopterygidae we observed that there were two larval cases with larvae, one located on the sternum and another on the prothoracic leg.Empty larval cases were recorded in 40% of the hosts (Tab.I).
The number of larvae without larval cases was significantly higher than that of larvae with larval cases (p< 0.05) in both seasons of the analysis (Fig. 3).In the rainy season, only a single Odonata specimen with a case of phoresy by Chironomidae was found.The mean velocity of the water and the outflow were significantly higher (p < 0.05) in the rainy season, possibly increasing the carrying of vegetal debris and their associated organisms, and thus making the phoretic association more difficult during this period.However, CALLISTO & GOULART (2000) recorded a higher number of Nanocladius sp.larvae (Chironomidae) in phoresy with nymphs of Ephemeroptera in the rainy season, relating this fact to the dispersion of vegetal debris in the studied stream.
Rheotanytarsus sp. has already been recorded from Brazil in association with Odonata larvae of Aeshnidae, Coenagrionidae,  STRIXINO 2003, ROQUE et al. 2004).The phoretic association of this chironomid with the Calopterygidae is herein for the first time recorded from Brazil.The phoretic association was observed in mesohabitats of litter in riffle areas and sediment in pool areas, possibly because the accumulation of leaves in these areas makes possible the maintenance of a greater abundance of invertebrates.Such abundance is related to the stability of the substrate and to the significant amount of debris (HYNES 1970).These conditions result in a greater availability of hosts to Rheotanytarsus sp.larvae, making possible the establishment of the phoretic association (TOKESHI 1993).
Rheotanytarsus sp. is a filter-feeding organism (COFFMAN & FERRINGTON 1984), which usually builds its tubes in lotic waters (SANSEVERINO & NESSIMIAN 2001).The individuals find in  Odonata larvae an appropriate body surface to the setting of their tubes and the accomplishment of their physiological and behavioral activities (SANSEVERINO et al. 1998).
Calopterygidae larvae and Heteragrion sp.larvae live in lotic habitats and they can be found in riffle areas and pool areas (CARVALHO & NESSIMIAN 1998) with a lot of marginal vegetation (FERREIRA-PERUQUETTI & DE MARCO 2002, COSTA et al. 2004, DE MARCO & PEIXOTO 2004).The establishment of the phoretic association between Chironomidae and Odonata, reported in the present work, may be related to the co-occurrence of the organisms in habitats with similar physical characteristics.
The results obtained in the present study suggest, even with the relatively low percentage of the phoretic relation observed, that Odonata larvae represent steady substrates for Rheotanytarsus sp., providing an increase in the mobility and in the capacity of the chironomid of exploring the environment (TOKESHI 1993, DOSDALL & PARKER 1998).Moreover, although Rheotanytarsus sp. is considered a commensalist without preference for a specific host (TOKESHI 1993), the results of this study indicate a possible preference for larvae of Odonata as the hosts, since the latter were found in the stream in a lower percentage in relation to other potential hosts.

Figure 3 .
Figure 3. Number of Odonata larvae with and without cases of phoresy by Rheotanytarsus sp.collected in the dry season of 2007 and in the rainy season of 2008 in a first-order stream in southeastern Brazil.
2Corresponding author.E-mail: beatrizjabour@yahoo.com.brABSTRACT.In this note, the occurrence of phoresy between larvae of Rheotanitarsus sp.(Diptera: Chironomidae) and larvae of Heteragrion sp.(Odonata: Megapodagrionidae) and of unidentified genera of Calopterygidae (Odonata) collected in a first-order stream in an area of Atlantic Forest in southeastern Brazil is reported.During the dry season of 2007 and the rainy season of 2008, with the aid of a Surber sampler, 15 samples of each of the following mesohabitats were collected: litter from riffle areas, litter from pool areas and sediment in pool areas.Eighty-five Odonata larvae were obtained, 10 (11.76%) with cases of phoresy by Rheotanytarsus sp..These chironomids were associated with only one specimen of Megapodagrionidae, whereas the other larvae were recorded in association with Calopterygidae.Most of the Odonata with cases of phoresy by Rheotanytarsus sp. were recorded in the dry season.In the present study, the absence of the phoretic association with other potential hosts for Rheotanytarsus sp.found in the samples indicates a possible preference of these larvae for Odonata, which accounted for only 2.42% of the collected macroinvertebrates in litter and sediment.KEY WORDS.Calopterygidae; Heteragrion; mesohabitats.ZOOLOGIA 26 (4): 787-791, December, 2009 washed

Table I .
Rheotanytarsus sp.associated to Odonata larvae found in a first-order stream in an area of Atlantic Forest, state of Minas Gerais, southeastern Brazil.It was not possible to distinguish the genera Hetaerina Hagen inSelys, 1853 and Mnesarete Cowley, 1934 (Calopterygidae).See text for details.Phoretic association between larvae of Rheotanytarsus and genera of Odonata *