Abstract
Coexistence of highly similar species is at odds with ecological theory of competition; coexistence, then, requires stabilizing mechanisms such as differences in ecological niche. In the bacterivore nematode Litoditis marina species complex, which occurs associated with macro-algae, four cryptic lineages (Pm I-IV) co-occur in the field along the south-western coast and estuaries of The Netherlands. Here we investigate the temporal and/or spatial niche differentiation in their natural environment using a qPCR-based detection and relative quantification method. We collected different algal species (i.e. two Fucus species and Ulva sp.) and separated algal structures (i.e. receptacula, thalli, non-fertile tips and bladders) at different sampling months and times (i.e. twice per sampling month), to examine differences in microhabitat use between coexisting L. marina species. Results demonstrate that the cryptic species composition varied among different algal species and algal structures, which was also subject to temporal shifts. Pm I dominated on Fucus spp., Pm II showed dominance on Ulva sp., while Pm III overall had the lowest frequencies. Microhabitat partitioning was most pronounced between the two cryptic species which had similar microbiomes (Pm I and Pm II), and less so between the two species which had significantly different microbiomes (Pm I and Pm III), suggesting that species which share the same microhabitats may avoid competition through resource partitioning. The interplay of microhabitat differentiation and temporal dynamics among the cryptic species of L. marina implies that there is a complex interaction between biotic components and abiotic factors which contributes to their coexistence in the field.
Highlights
Most estimates of biodiversity rely on inventories of morphologically identifiable species
Our results indicated that the cryptic species composition of the L. marina complex varied among different algal species and algal structures, patterns which were subject to temporal shifts
Using real-time quantitative PCR (qPCR), we demonstrate that the cryptic species composition of the Litoditis marina complex on macroalgae varies among different species of macroalgae, and among different structures of a particular algal species, which indicates that a single macroalga represents a spatially heterogeneous habitat
Summary
Most estimates of biodiversity rely on inventories of morphologically identifiable species. In the past two decades, the prominence of cryptic species, i.e. morphologically (nearly) identical but genetically distinct species, in many taxa has challenged existing estimates of biodiversity. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the abstract
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