Differential response to heat stress among evolutionary lineages of an aquatic invertebrate species complex (original) (raw)

Abstract

Under global warming scenarios, rising temperatures can constitute heat stress to which species may respond differentially. Within a described species, knowledge on cryptic diversity is of further relevance, as different lineages/cryptic species may respond differentially to environmental change. The Brachionus calyciflorus species complex (Rotifera), which was recently described using integrative taxonomy, is an essential component of aquatic ecosystems. Here, we tested the hypothesis that these (formerly cryptic) species differ in their heat tolerance. We assigned 47 clones with nuclear ITS1 (nuITS1) and mitochondrial COI (mtCOI) markers to evolutionary lineages, now named B. calyciflorus sensu stricto (s.s.) and B. fernandoi . We selected 15 representative clones and assessed their heat tolerance as a bi-dimensional phenotypic trait affected by both the intensity and duration of heat stress. We found two distinct groups, with B. calyciflorus s.s. clones having higher heat toleran...

Key takeaways

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  1. Brachionus calyciflorus s.s. shows higher CT max values (>40°C) than B. fernandoi under heat stress.
  2. The study reveals significant differences in heat tolerance among two cryptic lineages of B. calyciflorus.
  3. Forty-seven clones were genetically characterized using nuITS1 and mitochondrial COI markers.
  4. Heat tolerance is influenced by both temperature intensity and exposure duration, measured as LT 50.
  5. Understanding heat tolerance in cryptic species aids predictions of responses to global warming.

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FAQs

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What explains the difference in heat tolerance between the two Brachionus species?add

The study finds that B. calyciflorus s.s. exhibited significantly higher heat tolerance (CT max >40°C) compared to B. fernandoi, indicating specialized adaptation to thermal conditions.

How were genetic markers used to differentiate between Brachionus species?add

Nuclear and mitochondrial markers, notably nuITS1 and mtCOI, successfully assigned clones to B. calyciflorus s.s. and B. fernandoi, revealing new haplotypes and cryptic diversity.

What role does temperature play in the distribution of Brachionus lineages?add

The research indicates that seasonal distribution of B. calyciflorus is temperature-dependent, with co-occurrence of species occurring at intermediate temperatures around 16°C.

When did significant differences in thermal death time (LT50) become evident?add

Differences in LT50 were highly significant (p < 0.001) with temperature, particularly showing that B. calyciflorus s.s. survived heat stress longer across tested temperatures.

What methodology was employed to assess heat tolerance in Brachionus clones?add

The study utilized thermal death time (TDT) curves based on heat stress exposure, measuring knockdown time to determine heat tolerance across 30-36 individuals per clone.