Table S1. Origin of specimens used in the analysis. Species Origin and date of collection Specimen code Date of observation Date of freezing Niphargus croaticus Siničić pećina (cave),
1. Identifying the relationships between morphology and trophic niche is at the core of functional morphology. Low resource diversity and fluxes of organic carbon are expected to constrain trophic specialisation of morphological structures because food resources are too scarce to promote trophic differentiation. However, species from low-productivity habitats often exhibit specialised biological traits such as resistance to starvation and high food-finding abilities, which may in turn release constraints on trophic and morphological differentiation among species.2. Groundwaters are food resource-limited because of the lack of photosynthetic production and limited inputs of organic carbon from surface ecosystems. We tested for co-variation between morphology and trophic habits in co-occurring Niphargus amphipods from five groundwater caves of the Dinaric Karst, Europe.We predicted that the size of gnathopods-the accessory feeding appendageswould positively co-vary with trophic position: species with larger gnathopods should more easily grab and immobilise prey.3. We quantified gnathopod size and shape by means of morphometric measurements and assessed isotopic niche, trophic position, and carbon signatures using nitrogen (δ 15 N) and carbon (δ 13 C) stable isotopes. We tested for correlation between morphological traits and trophic position and δ 13 C signatures while accounting for phylogenetic relationships among species. 4. All co-occurring species differed morphologically in at least one gnathopod measurement and all of them differed in their isotopic niches. As predicted, gnathopod size increased with the increasing trophic position. This co-variation probably reflects differences in detritivorous and predatory habits among species: amphipods with larger gnathopods, hence larger muscle and more powerful grip, could more easily subdue prey. Moreover, we found a significant correlation between gnathopod shape and the normalised δ 13 C values, indicating that shape of the gnathopods may be related to exploitation of different food resources.5. We show that low-productivity subterranean habitat species can exhibit strong trophic specialisation of morphological structures. Gnathopod size and shape of Niphargus amphipods are functional traits that co-vary with trophic habits. Our | 1877 PREMATE ET Al.
To tackle climate change, environmental degradation and biodiversity loss, the European Commission (EC) initiated the European Green Deal (EGD) in 2021, designed to achieve a sustainable and carbon neutral economy by 2050 1 . An important action within the EGD is the Biodiversity Strategy for 2030 (BS2030), a comprehensive plan for protecting nature, reversing degradation of ecosystems, and securing ecosystem services 2 . Biodiversity protection is considered essential for a successful implementation of the EGD, and the program is designed such that actions should also not harm biodiversity outside the EU 1 . These are laudable and necessary aims, but we argue that some actions of the EDG collide with its goal of protecting biodiversity. This is particularly evident when considering the effects of planned hydropower development on subterranean biodiversity in the Western Balkans.Hydropower is a source of renewable energy, yet it is often not sustainable. Devastating effects of hydropower on aquatic and riparian biotas have been documented 3 . While the BS2030 aims to restore 25,000 km of rivers in some parts of the EU, an action that includes dam removal 2 , paradoxically, there are extensive plans to build new hydropower plants in other parts. These pressures are especially strong in the Western Balkans 4 , where many rivers are still free-flowing and are waterways are considered an
Predator–prey interactions are among the most important biotic interactions shaping ecological communities and driving the evolution of defensive traits. These interactions and their effects on species received little attention in extreme and remote environments, where possibilities for direct observations and experimental manipulation of the animals are limited. In this paper, we study such type of environment, namely caves of the Dinarides (Europe), combining spatial and phylogenetic methods. We focused on several species of Niphargus amphipods living in phreatic lakes, as some of them use the dorsal spines as putative morphological defensive traits. We predicted that these spines represent a defense strategy against the olm (Proteus anguinus), a top predator species in the subterranean waters. We tested for spatial overlap of the olm and Niphargus species and showed that spined species live in closer proximity to and co-occur more frequently with the olm than non-spined species. Modeling of the evolution of the spines onto Niphargus phylogeny implies coevolution of this trait in the presence of olm. We conclude that these spines likely evolved as defensive traits in a predator–prey arms race. Combining multiple analyses, we provide an example for a methodological framework to assess predator–prey interactions when in-situ or laboratory observations are not possible.
Cave animals are biological models of fast evolutionary change induced by transition to extreme subterranean environments. But their concealed lifestyle makes it inherently difficult to study life-history changes. Therefore, currently very little is known on the reproduction of cave species, and even less is known on general patterns and potentially shared reproductive strategies. Theory predicts that the cave environment favours the production of a few well-developed offspring and live birth. For one of the most enigmatic cave animals, the olm (Proteus anguinus), it has been debated fiercely whether they reproduce by live birth (viviparity), egg-laying (oviparity) or facultatively. While successes in captive breeding after the 1950s report oviparity as the single parity mode, some historically older observations claimed viviparity. The controversial neo-Lamarckist Paul Kammerer even claimed to have induced changes in parity mode by altering environmental conditions. Here, we report on the feeding and regurgitation of fire salamander (Salamandra salamandra) larvae by olms. The salamander larvae showed clear teeth marks and other injuries on the head caused by the olm, yet one larva was still alive after regurgitation. We suggest that historical reports of olm viviparity could have been misled by regurgitated salamander larvae. Our data bring additional indications that at least some of Kammerer’s experiments were fraudulent.
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