Arachnologische Mitteilungen 57

Diaspores as food for spiders 35 the periphery of the web of Agelena labyrinthica , all of them were found closer to the center after 3–4 days. Due to the small number of tested spider individuals, these observations are not necessarily conclusive, but they at least show a trend indicating that different spider species may differ in their pro- pensity to consume myrmecochorous diaspores. Discussion Elaiosomes, as juicy or fleshy appendages of diaspores, can be formed from various tissues of seeds, fruits or even other plant parts. Their chemical composition is quite different from all other plant structures (Leins & Erbar 2010). According to Fisher et al. (2008), elaiosomes of 15 plant species from seven different families were more similar to each other than each was to the other seed parts of the same species.The high nu- tritional value of elaiosomes is related especially to fats and sugars, but they also contain proteins, vitamins and other sub- stances (Leins & Erbar 2010). Some of these chemicals have signalling effects on ants. For example diglyceride 1,2-diolein, which is also a component of insect hemolymph, is supposed to be the main signalling compound for ants collecting dia- spores with elaiosomes (Rico-Gray & Oliveira 2007). Even purely carnivorous ant species, which usually avoid plant resources, are attracted to elaiosomes whose composition is more similar to insects than other plant tissues (Hughes et al. 1994). This is probably the reason why some spiders, which are otherwise obligate predators, can consume myrmecocho- rous diaspores. During plant evolution, elaiosomes appeared in many in- dependent events after ants started to dominante terrestrial ecosystems (Dunn et al. 2007, Lengyel et al. 2010). It proved advantageous for many plant species to distribute themsel- ves with the help of these omnipresent ant predators. Such plants evolved diaspores equipped with imitations of insect prey (elaiosomes as a reward for ants). This is usually a mu- tually advantageous relationship in which ants transport dia- spores, utilise highly nutritional elaiosomes and leave the rest of diaspores untouched in more or less remote sites.Therefore myrmecochory could arise from exploitation of predator–prey relationships (Fenner &Thompson 2005). Formation of such structures by plants was ‘targetted’ towards omnivorous and carnivorous ants so that they would distribute diaspores, but other generalist predators such as some ground beetles (Oha- ra & Higashi 1987) can use this resource as well. Animals consuming elaiosomes without dispersing the seeds disrupt ant–plant mutualism (Rico-Gray & Oliveira 2007) and, as is shown in this paper, some spiders can be included – from an ecological point of view – in this disruptive group too. As shown here, spiders can consume diaspores with elai- osomes. Another question is how widespread this phenome- non is in the natural environment? In the case of Uloboridae it does not probably occur, because such diaspores would ra- rely get into their webs. But in the case of Theridiidae, with threads attached to the ground, it is more probable. Especially when a web is constructed near the source plants, or above ant trials where diaspores are transported. Many Theridiidae spe- cies catch ants using sticky threads anchored to the substra- te. Even in our greenhouses, individuals of all the common ant species [ Lasius niger (Linnaeus, 1758), Lasius brunneus (Latreille, 1798), Lasius emarginatus (Olivier, 1792), Campo- notus fallax (Nylander, 1856), Tetramorium sp.] were docu- mented as prey of P. tepidariorum or P. tabulata . Workers of the same spectrum of ant species readily grab the myrmeco- chorous seeds on offer. In the context of the above findings, a spider could consume both a worker ant and the seed carried along and abandoned after attack. Direct observation of such activities is missing so far, but the simultaneous occurrence of seeds and ants in the web was registered (Fig. 5). Overall, it seems to be another example of tritrophic interactions betwe- en spiders, plants and ants.The possible interactions of some Theridiidae spiders with myrmecochorous plants and ants are not as specific as in the salticid Bagheera kiplingi on Vachellia sp. acacias with Pseudomyrmex sp. ants (Meehan et al. 2009). Nyffeler et al. (2016) documented spiders feeding on plant materials representing about 20 different plant families. In the current paper, it is shown that spiders feed on plant materials representing five additional families (Amaryllida- ceae, Aristolochiaceae, Costaceae, Papaveraceae and Ranun- culaceae). Considering high number of other non-tested myrmecochorous plants and spiders, other families might be expected to supplement this list. On the one hand, there may be differences in detailed chemical composition of elaiosomes in individual plant species, on the other, there are various food strategies and preferences of spiders with different opportu- Fig. 5: Simultaneous occurrence of two seeds of Costus dubius and a worker of Lasius brunneus in the web of Parasteatoda sp. spider with the code P16, 15.I.2018 (see text and Fig. 1 for other details), above sill in a greenhouse of BG PJŠU. In this case the prey was captured by a resident spider after an ant worker was coming here, either accidentally or attracted to the intentionally placed seeds (by the experimentator) on the sill (and, previously, some seeds were picked up by a spider). Under natural conditions the opposite situation may be more likely – seeds could be brought below spider web by ants the- meselves and afterwards (after the killing ants) these seeds could be pulled up by the spiders.