Otus

4.1. General relationships between OTUs View in CoL

There were obvious differences between D. ghetaldii from the five karst fields relative to their head shape (both length and width) and certain other morphometric characteristics (Appendix 1). Comparing to the literature, Dekić et al.

(2017) stated that D. ghetaldii from the Fatničko and Ljubomirsko karst fields are different from each other in morphometry, while Mustafić et al. (2016) stated the same for those from the Dabarsko and Fatničko karst fields. The characteristics that exert the most substantial influence on the interspecies variation in the Dabarsko and Fatničko karst fields are body height and head length, which is in line with Mustafić et al. (2016). Although the ecological features of those localities differ, subterranean migrations have been postulated but never examined in detail. Our analysis by UPGMA clustering revealed a morphological similarity between the D. ghetaldii of the Dabarsko and Ljubomirsko OTUs , as well as between those of the Mokro and Fatničko OTUs ( Figure 4 View Figure 4 ).

It is indicative that particular morphometric characteristics that had unique variability, meaning deviation from the normal distribution when tested univariately, were prominent in discrimination. For example, horizontal eye diameter had the greatest discrimination power at discriminant root 2. It distinguished the OTUs of the Mokro and Fatničko karst fields and, in combination with interorbital width, determined the similarity between the two main clusters comprising OTUs of the other karst fields. Likewise, maximum head width distinguished OTUs of the Dabarsko and Popovo karst fields from all others. None of the characteristics remarkable in sex differentiation deviated significantly from normal distribution, nor did they have great overall discrimination power, indicating weak sexual dimorphism in D. ghetaldii .

4.2. Correspondence between geology and morphology Until the 1960s, the Trebišnjica River stood as Europe’s longest sinking river and was possibly among the longest worldwide. It was a complex system of 326 km of interconnected river courses that extended from its source at Dobra Voda to Čemerna and ended in a confluence with the Dubrovnik River, which flowed into the Adriatic Sea. The confluence of the Krupa River with the Neretva River was also part of this intricate system. Along the way, the course alternated between submerged and resurgent stretches. Local inhabitants, unaware of the connections between these segments, bestowed distinct names upon each of these segments ( Banjak, 2016). From the Viduša peaks, the confluence descended into the Fatničko karst field, where an underground bifurcation occurred ( Milanović, 1979) and those sinking waters split into two branches, one directed toward the Trebišnjica basin and the other toward the Neretva River. This bifurcation appears to explain the similarity observed between D. ghetaldii OTUs from the Fatničko and Mokro karst fields. Notably, the Dabarsko karst field is a part of the drainage systems of both the Neretva and Trebišnjica rivers. The most significant sinkhole in this field is the Ponikva. The Vrijeka River, receiving the tributary Pribitul River, constitutes the primary watercourse that disappears in the Ponikva sinkhole ( Pecelj, 1989). In the Ljubomirsko karst field, an underground connection to springs exists along the right bank of the Trebišnjica River. The resemblance of OTUs from these locations could be attributed to the sampling sites at the Vrijeka River in the Dabarsko karst field and at the Ljubomirski stream in the Ljubomirsko karst field, both of which have surface-flowing streams. This stands in contrast to the other fields, where D. ghetaldii individuals were sampled directly from inundated fields as they emerged due to cave precipitation or estavelles. D. ghetaldii of the Dabarsko karst field exhibits some shared continuous morphological characteristics, such as horizontal eye diameter and postorbital distance, with those from the Ljubomirsko karst field (Appendix 2). However, the most distinctive and isolated OTU arises from the Popovo karst field. Morphological differences among D. ghetaldii individuals from the Popovo field, especially in head length, maximum head width, interorbital width, and horizontal eye diameter, lend support to the notion of greater similarity between the OTUs of the Mokro and Fatničko karst fields compared to the OTUs of the Dabarsko and Ljubomirsko karst fields ( Figure 4 View Figure 4 ). This conclusion aligns with Steindachner (1882), who initially identified and described this species as Paraphoxinus ghetaldii while delineating another species in the Popovo karst field as Paraphoxinus pstrossi . Hence, he recognized a distinction between species from the Popovo karst field and those from other Eastern Herzegovina karst fields. This distinction persisted until recent molecular analyses, in which Palandačić et al. (2010), utilizing nuclear DNA sequences, established that D. ghetaldii of the Ljubomirsko karst field form a sister group to the D. ghetaldii populations in the Popovo karst field. The lower course of the Trebisnjica River flows through the Popovo karst field, which is different from other karst fields because it “bends with numerous curves”, like a valley of “every other ordinary river” ( Absolon, 1916), which correlates with the testimony of Cvijić (1918) that this karst field is a “pure result of river flow” ( Spahić, 2015).