New records of a poorly studied mayfly species, Eurylophella karelica Tiensuu, 1935 (Ephemeroptera, Ephemerellidae), in the Baltic Ecoregion

Eurylophella karelica is a rare and poorly investigated species of European Ephemeroptera from the family Ephemerellidae. From the 1930s to 1970s, E. karelica has not been reported from historical localities in Karelia, Lithuania and Poland. New localities from Hungary, Slovenia and Lithuania are discovered over the last 2 decades. This article reports first findings of E. karelica in Latvia and Estonia and explains sporadic distribution of this species.


Introduction
In Europe, the genus Eurylophella Tiensuu, 1935 is represented by three species (Martynov et al. 2015).Eurylophella karelica was the first species described in this genus (Tiensuu 1935).Eurylophella iberica is endemic to Iberian Peninsula (Keffermüller and Da Terra 1978) and E. korneyevi was recently described from Caucasus region of Georgia (Martynov et al. 2015).Overall, genus Eurylophella has a Holarctic distribution with 19 valid species (Burian 2002, Bauernfeind and Soldán 2012, Martynov et al. 2015).
Little is known regarding biology and ecology of E. karelica (Bauernfeind and Soldán 2012).Larvae were found in slow-flowing stretches of rivers and brooks (Kazlauskas 1959, Sowa 1961), as well as in lakes (Keffermüller 1960).Stones, gravel, clay (Tiensuu 1935), submerged macrophytes, roots of riparian vegetation, organic debris (Kovács and Ambrus 1999) and muddy sediment (Sowa 1961) were observed as their preferred habitats.Details of its life cycle are not thoroughly reported.Larvae have been found in late summer, autumn and spring but not in early and mid-summer (Tiensuu
This article reports first records of E. karelica (Fig. 1) in Latvia and Estonia, additionally, clarifying disjunctive distribution of the species.

Methods
Our study comprises 1) the database of Institute of Biology, University of Latvia, 2) the data of surface water monitoring programme in Latvia, from 2007 to 2013 performed by Latvian Environment, Geology and Meteorology Centre, and 3) the data of E. karelica localities in Estonia, provided by Estonian University of Life Sciences.
The larvae of E. karelica in Latvia and Estonia were found in autumn (September-November) and spring (April-May) in lowland streams and rivers.In Latvia, the larvae were found in 9 localities of 7 watercourses, while in Estonia, in 10 watercourses, and exceptionally, in the littoral zone of a Lake Tündre (Table 1).

Material examined. Table 1.
The main characteristic differentiating larvae in genus Eurylophella are the shape of the paired tubercles on abdominal terga (Allen and Edmunds 1963).In E. karelica, tubercles are long, blunt or moderately sharp on segments 1-3, long and sharp on segments 4-7 and short, barely discernible or absent on segments 8-10 (Fig. 1).Nymphs of E. karelica were identified using published keys (Allen and Edmunds 1963, Bauernfeind and Soldán 2012, Martynov et al. 2015).Species identification was approved by Dr Henn Timm from Estonian University of Life Sciences.

Discussion
Nymphs of E. karelica were reported from waterbodies situated on plains (Tiensuu 1935, Kazlauskas 1959, Keffermüller 1960, Sowa 1961, Kovács and Ambrus 1999, Kovács et al. 2008).Lithuania, Latvia and Estonia are located in the Baltic Province (Ecoregion No. 15), which also is a lowland area (Illies 1978).Thus, we suggest that E. karelica is a lowland species, as it is shown on the distribution map (Fig. 2).The new localities are the first records of E. karelica in Estonia and Latvia.Within the Baltic region, they were previously reported only in Lithuania.The record from the littoral zone of Lake Tündre in Estonia was the second case from the lentic habitat since Keffermüller (1960) found E. karelica in Lake Góreckie, a post-glacial, mesotrophic lake in Poland.
The data corroborated earlier reports, which regard E. karelica as a relict of the last Ice Age (Keffermüller 1960, Kovács andAmbrus 1999).The absence of nymphs during the summer sampling could be caused either by summer egg diapause or by larvae being too small to be detected by routine sampling methods (Bohle 1972, Brittain 1982).A summer egg diapause have been discussed in North American species of the genus Eurylophella (Hamilton and Tarter 1977).However, detailed life cycle studies of E. karelica are required to justify these statements.The distribution of E. karelica was considered sporadic with small refugial areas (Kovács and Ambrus 1999).The current findings suggest that this species is more widespread than it was previously predicted.The reasons for this could be inappropriate sampling season (summer) to detect the larvae or absence of the research.Nevertheless, E. karelica mostly occurred in small numbers at the reported sampling sites (Tiensuu 1935, Kazlauskas 1959, Keffermüller 1960, Kovács and Ambrus 1999) suggesting relatively low abundances within its habitats.According to Kovács and Ambrus 1999, May is the proper sampling season for adults.
We assume that E. karelica inhabit a wider range of European lowland watercourses than expected before.However, appropriate sampling season (autumn to spring) should be considered first to improve the distribution pattern of this species.