Constant diversification rates of endemic gastropods in ancient Lake Ohrid: ecosystem resilience likely buffers environmental fluctuations

[摘要] Ancient lakes represent key ecosystems for endemic freshwater species. Thishigh endemic biodiversity has been shown to be mainly the result ofintra-lacustrine diversification. Whereas the principle role of this mode ofdiversification is generally acknowledged, actual diversification rates inancient lakes remain little understood. At least four types are conceivable.Diversification rates may be constant over time, they may fluctuate, ratesmay be higher in the initial phase of diversification, or there may be apronounced lag phase between colonization and subsequent diversification. Asunderstanding the tempo of diversification in ancient lake environments mayhelp reveal the underlying processes that drive speciation andextinction, we here use the Balkan Lake Ohrid as a model system and thelargest species flock in the lake, the non-pyrgulinid Hydrobiidae, as amodel taxon to study changes in diversification rates over time togetherwith the respective drivers.

Based on phylogenetic, molecular-clock, lineage-through-time plot, anddiversification-rate analyses we found that this potentially monophyleticgroup is comparatively old and that it most likely evolved with a constantdiversification rate. Preliminary data of the SCOPSCO (Scientific Collaboration On Past Speciation Conditions in Lake Ohrid) deep-drilling programdo indicate signatures of severe environmental/climatic perturbations inLake Ohrid. However, so far there is no evidence for the occurrence ofcatastrophic environmental events. We therefore propose that the constantdiversification rate observed in endemic gastropods has been caused by twofactors: (i) a potential lack of catastrophic environmental events in LakeOhrid and/or (ii) a probably high ecosystem resilience, bufferingenvironmental changes. Parameters potentially contributing to the lake'shigh ecosystem resilience are its distinct bathymetry, ongoing tectonicactivities, and karst hydrology.

The current study not only contributes to one of the overall goals of theSCOPSCO deep-drilling program – inferring the driving forces for bioticevolution in Lake Ohrid. It might also enhance our understanding of howecosystem resilience, in general, may promote relatively constantdiversification rates in isolated ecosystems. However, we encourage futurestudies testing hypotheses about the lack of catastrophic events in LakeOhrid. These studies should be based on high-resolution data for the entiregeological history of the lake, and they should potentially involve information fromthe sediment fossil record, not only for gastropods but also for othergroups with a high share of endemic taxa.

[学科分类] 地球化学与岩石