Research Unit for Evolutionary Immunogenomics, Department of Biology, University of Hamburg, Martin-Luther-King-Platz 3, Hamburg, Germany.
Faculty of Medicine, University of São Paulo, Av. Dr. Arnaldo, 455 - Cerqueira César, Pacaembu, 01246-903, São Paulo, Brazil.
BMC Ecol Evol. 2024 Sep 20;24(1):122. doi: 10.1186/s12862-024-02305-3.
Hybrids are expected to show greater phenotypic variation than their parental species, yet how hybrid phenotype expression varies with genetic distances in closely-related parental species remains surprisingly understudied. Here, we investigate pelage and morphometric trait variation in anthropogenic hybrids between four species of Brazilian Callithrix marmosets, a relatively recent primate radiation. Marmoset species are distinguishable by pelage phenotype and morphological specializations for eating tree exudates. In this work, we (1) describe qualitative phenotypic pelage differences between parental species and hybrids; (2) test whether significant quantitative differences exist between parental and hybrid morphometric phenotypes; and (3) determine which hybrid morphometic traits show heterosis, dysgenesis, trangression, or intermediacy relative to the parental trait. We investigated cranial and post-cranial morphometric traits, as most hybrid morphological studies focus on the former instead of the latter. Finally, we estimate mitogenomic distances between marmoset species from previously published data.
Marmoset hybrid facial and overall body pelage variation reflected novel combinations of coloration and patterns present in parental species. In morphometric traits, C. jacchus and C. penicillata were the most similar, while C. aurita was the most distinct, and C. geoffroyi trait measures fell between these species. Only three traits in C. jacchus x C. penicillata hybrids showed heterosis. We observed heterosis and dysgenesis in several traits of C. penicillata x C. geoffroyi hybrids. Transgressive segregation was observed in hybrids of C. aurita and the other species. These hybrids were also C. aurita-like for a number of traits, including body length. Genetic distance was closest between C. jacchus and C. penicillata and farthest between C. aurita and the other species.
We attributed significant morphometric differences between marmoset species to variable levels of morphological specialization for exudivory in these species. Our results suggest that intermediate or parental species-like hybrid traits relative to the parental trait values are more likely in crosses between species with relatively lesser genetic distance. More extreme phenotypic variation is more likely in parental species with greater genetic distance, with transgressive traits appearing in hybrids of the most genetically distant parental species. We further suggest that fewer developmental disturbances can be expected in hybrids of more recently diverged parental species, and that future studies of hybrid phenotypic variation should investigate selective pressures on Callithrix cranial and post-cranial morphological traits.
杂种预计会表现出比其亲本物种更大的表型变异，但杂种表型表达如何随亲缘关系密切的亲本物种的遗传距离而变化，这仍然令人惊讶地研究不足。在这里，我们调查了巴西狨猴四种近缘种间人为杂交种的皮毛和形态特征变异，这是灵长类动物最近的辐射。狨猴物种通过皮毛表型和专门用于吃树液的形态特征来区分。在这项工作中，我们 (1) 描述了亲本物种和杂种之间定性表型皮毛差异；(2) 测试了亲本和杂种形态表型之间是否存在显著的定量差异；(3) 确定了相对于亲本性状，哪些杂种形态特征表现出杂种优势、杂种不育、杂种越界或杂种中间型。我们调查了颅后形态特征，因为大多数杂种形态学研究集中在前者而不是后者。最后，我们根据之前发表的数据估计了狨猴物种的线粒体基因组距离。
狨猴杂种面部和整体身体皮毛变化反映了亲本物种中存在的颜色和图案的新组合。在形态特征方面，C. jacchus 和 C. penicillata 最为相似，而 C. aurita 最为独特，C. geoffroyi 的特征介于这两个物种之间。C. jacchus x C. penicillata 杂种中只有三个特征表现出杂种优势。我们观察到 C. penicillata x C. geoffroyi 杂种的几个特征出现杂种不育和杂种越界。C. aurita 与其他物种的杂种出现了杂种优势和杂种不育。这些杂种在许多特征上也类似于 C. aurita，包括体长。遗传距离在 C. jacchus 和 C. penicillata 之间最接近，在 C. aurita 和其他物种之间最远。
我们将狨猴物种之间的显著形态差异归因于这些物种对分泌液的形态特化程度不同。我们的结果表明，在遗传距离相对较小的物种之间杂交，相对于亲本性状值，杂种具有中间型或亲本型特征的可能性更大。在遗传距离较大的亲本物种中，更可能出现极端的表型变异，杂种中出现的越界特征出现在遗传距离最大的亲本物种中。我们进一步认为，在遗传上分化较新的亲本物种的杂种中，发育障碍可以预期更少，未来对杂种表型变异的研究应该调查对 Callithrix 颅后形态特征的选择压力。
