What happens when several pre-divergence lineages are mixed in one space? A minimal individual-based model of mating gates and search costs

[This data contains both English and Japanese preprint versions (Version 1.0.0) of a minimal individual-based model of mixing several pre-divergence lineages, together with the simulation code.] ■ Abstract In organisms whose mating depends on the period or timing of activity, it matters how lineages fuse, and which persist, when several lineages that have not yet fully diverged are mixed in one space. We built a minimal individual-based model that keeps only the mating gate (how mates are accepted as a function of the difference in period), increased the initial number of lineages N from 2 to 10, and examined how many clusters finally remained. Under the model's assumptions, the following predictions were obtained. (1) The number of remaining clusters did not scale with N and was at most 2–4. (2) It was hump-shaped in preference width: with narrow preferences only one lineage remained, with wide preferences everything fused, and several clusters remained only at intermediate widths. (3) At wide preferences, the soft Gaussian gate led to fusion because of its tail, whereas a hard window did not. (4) The results depended strongly on the efficiency of mate search, and with a search cost almost no clusters remained under the Gaussian gate. In addition, in a minimal model of a new species diverging again, when broken alleles are lost easily and restored with difficulty, the longer the population had spent as the new species, the slower its return to the ancestral state. These are assumption-dependent predictions and have not been calibrated against empirical data. We propose predictions that can be tested in captivity. 【本資料は、分化前の複数系統を同じ空間に混ぜたときの最小個体ベースモデルのプレプリント論文(Version 1.0.0)の日本語版と英語版、およびシミュレーションコードです】 ■ 要旨 周期や活動時期で配偶者が決まる生物では、分化しきる前の複数の系統を同じ空間に混ぜたとき、系統がどう融合し、どれが残るかが問題になる。本稿は、周期の差に対する受け入れ方(配偶ゲート)だけを残した最小の個体ベースモデルを作り、初期の系統数Nを2〜10に増やして、最終的に残るまとまりの数を調べた。モデルの仮定のもとで、次の予測が得られた。(1) 残るまとまりの数はNに比例せず、最大で2〜4にとどまった。(2) 選好の幅に対して山型になり、狭いと1系統だけが残り、広いと全体が融合し、複数のまとまりが残るのは中間の幅だけだった。(3) 広い側では、ゆるやかなガウス型は裾野のために融合し、硬い窓型は融合しなかった。(4) 結果は相手探しの効率に強く依存し、探索コストを入れるとガウス型ではまとまりはほぼ残らなかった。さらに、新種が再び分化する場面の最小モデルでは、壊れやすく戻りにくいアレルの非対称があるとき、新種として過ごした期間が長いほど祖先への戻りが遅くなった。これらは仮定に依存した予測であり、実測による較正は未了である。飼育下で検証できる予測を示す。