ユスリカが月明かりの下で時空間を分割し共存する行動(Coexistence by Moonlight: How Midges Divide Time and Space)

2025-07-21 マックス・プランク研究所

An adult male of Clunio marinus (about 2 millimeters long). © Solvin Zankl

<関連情報>

• https://www.mpg.de/25083746/coexistence-by-moonlight-how-midges-divide-time-and-space
• https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2656.70094
• https://onlinelibrary.wiley.com/doi/10.1111/ele.70139

一時的なニッチ分化は、共存よりもむしろ優先効果をもたらすことが多い: 海洋性ユスリカからの教訓 Temporal niche differentiation often leads to priority effects rather than coexistence: Lessons from a marine midge

Runa K. Ekrem, Charlotte de Vries, Tobias S. Kaiser, Hanna Kokko
Journal of Animal Ecology  Published: 20 July 2025
DOI:https://doi.org/10.1111/1365-2656.70094

Abstract

1. While niche differences aid coexistence, the role of temporal niches is complex. A recent study (Stump & Vasseur, 2023) casts doubt on the idea that species coexist easily if they partition abiotic niches that vary in time. The storage effect, which aids coexistence, requires that species differ in what is a ‘good year’, and that the benefits that the currently common species can draw from its own good year become limited due to intraspecific competition.
2. The recent re-evaluation of temporal niches considered Allee effects only fleetingly. We complement their work by providing a case study of the marine midge Clunio marinus, where coexistence appears to occur in nature, is associated with a strong difference in timing traits, and also features Allee effects because rare timing phenotypes emerge with limited mating opportunities.
3. The larvae develop in the sea, and adults emerge and mate during the lowest low tides. These tides coincide with either the full or the new moon, and genetically determined strains use either one of them, or both, for emergence. A ‘good year’ in this system translates into a particular low tide. Allee effects create strain-specific good tides if the risk of hybridization is greater for the currently rare strain, which mates more often with another strain, than the currently common strain.
4. We are able to investigate this effect by varying the effects of hybridization in our model of Clunio biology. Temporal niches, mate-finding Allee effects, hybridization possibilities and a potential growth-survival tradeoff do not easily combine to yield stable coexistence. Most factors instead promote positive frequency dependence, leading to priority effects. Ontogenetic niche shifts among larvae deviate from this result: if suitably timed, they are able to concentrate competition in a coexistence-promoting manner.
5. Our study thus complements and strengthens Stump and Vasseur’s conclusion that a finding of temporal niche differentiation should not be straightforwardly assumed to be an explanation for the coexistence of two or more morphs or species. We encourage linking temporal niche studies with those of priority effects, as well as the study of other coexistence mechanisms that may operate within systems that feature temporal niches.

昆虫はいかにして時間を空間に変換するのか?時間的ニッチは繁殖に利用可能な生息地の量を変化させることで共存を助ける How an Insect Converts Time Into Space: Temporal Niches Aid Coexistence via Modifying the Amount of Habitat Available for Reproduction

Runa K. Ekrem, Alexander Jacobsen, Hanna Kokko, Tobias S. Kaiser
Ecology Letters  Published: 30 May 2025
DOI:https://doi.org/10.1111/ele.70139

ABSTRACT

Temporal niches do not automatically promote coexistence. We combine field data on the marine midge Clunio marinus with a model. In Roscoff (Brittany, France) sympatric C. marinus timing strains emerge at full moon (FM strain) or just before new moon (NM strain). We show that NM individuals reproduce and lay eggs when the water level is higher than during FM strain reproduction, and that this shift partially segregates larvae according to elevation. Modelling the underlying dynamics shows that the causality from temporal to spatial niches is crucial for coexistence: for hypothetical strains which differ in the temporal niche used for reproduction so that they use equivalently low water levels for egg-laying, the dynamics show priority effects, not coexistence. While general theory on temporal niches is rather complex, we highlight the understudied possibility that timing traits cause differences in space use, and coexistence is unproblematic as it results from spatial niches.