Mismatch between pollen and pistil size causes asymmetric mechanical reproductive isolation across Phlox species.

IF 3.1 2区 环境科学与生态学 Q2 ECOLOGY Evolution Pub Date : 2024-09-14 DOI:10.1093/evolut/qpae128
Anna F Feller, Grace Burgin, Nia Lewis, Rohan Prabhu, Robin Hopkins
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Abstract

Characterizing the mechanisms of reproductive isolation (RI) between lineages is key to determining how new species are formed and maintained. In flowering plants, interactions between the reproductive organs of the flower -the pollen and the pistil- serve as the last barrier to reproduction before fertilization. As such, these pollen-pistil interactions are both complex and important for determining a suitable mate. Here, we test whether differences in style length (a part of the pistil) generate a postmating prezygotic mechanical barrier between five species of perennial Phlox wildflowers with geographically overlapping distributions. We perform controlled pairwise reciprocal crosses between three species with long styles and two species with short styles to assess crossing success (seed set). We find that heterospecific seed set is broadly reduced compared to conspecific cross success and reveal a striking asymmetry in heterospecific crosses between species with different style lengths. To determine the mechanism underlying this asymmetric reproductive isolating barrier we assess pollen tube growth in vivo and in vitro. We demonstrate that pollen tubes of short-styled species do not grow long enough to reach the ovaries of long-styled species. We find that short-styled species also have smaller pollen and that both within and between species pollen diameter is highly correlated with pollen tube length. Our results support the hypothesis that the small pollen of short-styled species lacks resources to grow pollen tubes long enough to access the ovaries of the long-styled species, resulting in an asymmetrical, mechanical barrier to reproduction. Such reproductive isolating mechanisms, combined with additional pollen-pistil incompatibilities, may be particularly important for closely related species in geographic proximity that share pollinators.

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花粉和雌蕊大小的不匹配会导致凤仙花物种间不对称的机械生殖隔离。
描述不同品系之间的生殖隔离(RI)机制是确定新物种如何形成和维持的关键。在开花植物中,花的生殖器官--花粉和雌蕊--之间的相互作用是受精前生殖的最后一道屏障。因此,花粉与雌蕊之间的相互作用既复杂又对确定合适的配偶非常重要。在这里,我们测试了花柱长度(雌蕊的一部分)的差异是否会在地理分布重叠的五种多年生凤仙花野花之间产生交配前的机械障碍。我们在三个花柱较长的物种和两个花柱较短的物种之间进行受控的成对互交,以评估杂交成功率(结籽率)。我们发现,与同种杂交成功率相比,异种杂交的结籽率普遍较低,并揭示了不同花柱长度物种之间异种杂交的显著不对称性。为了确定这种不对称生殖隔离障碍的机制,我们对花粉管的体内和体外生长进行了评估。我们证明,短花柱物种的花粉管无法长到足以到达长花柱物种的子房。我们发现,短花柱物种的花粉也较小,而且在物种内部和物种之间,花粉直径与花粉管长度高度相关。我们的研究结果支持这样的假设:短花柱物种的花粉较小,缺乏足够长的花粉管资源来进入长花柱物种的子房,从而形成不对称的机械繁殖障碍。这种生殖隔离机制与其他花粉-雌蕊不相容的机制相结合,对于地理位置相近、共享授粉者的近缘物种来说可能特别重要。
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来源期刊
Evolution
Evolution 环境科学-进化生物学
CiteScore
5.00
自引率
9.10%
发文量
0
审稿时长
3-6 weeks
期刊介绍: Evolution, published for the Society for the Study of Evolution, is the premier publication devoted to the study of organic evolution and the integration of the various fields of science concerned with evolution. The journal presents significant and original results that extend our understanding of evolutionary phenomena and processes.
期刊最新文献
Shared environmental similarity between relatives influences heritability of reproductive timing in wild great tits. Correction to: Plasticity cannot fully compensate evolutionary differences in heat tolerance across fish species. Beyond Peto's Paradox: Expanding the Study of Cancer Resistance Across Species. Digest: Extremes of the mating system continuum are the most evolutionarily stable. Digest: Scarce pollen resources and asymmetric reproductive isolation.
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