Milkyway
06-04-2020, 07:38 AM
I found this study (https://royalsocietypublishing.org/doi/10.1098/rspb.2020.0690) interesting.
37874
Some pieces of information:
We first explicitly defined two dichotomous categories along the spectrum of hybrid incompatibility. Category 1 is defined by mammalian species pairs capable of producing fertile F1 offspring of both sexes that can reproduce without backcrossing with a parent species (even if there are observed asymmetries in gene flow and variation in male fertility among the hybrids) (electronic supplementary material, table S1). category 2 is defined by pairs of species that can produce viable F1 offspring, but follow Haldane's Rule, and thus only female F1s can reproduce by backcrossing with a parent species. category 2 also includes species pairs whose hybrids are infertile (electronic supplementary material, table S1).
The category 1 pair with the greatest divergence value was a pair of guinea pig species that were 8.0% divergent, and the category 2 pair with the lowest divergence was a pair of vole species that were 7.2% divergent. Several pairs of species fall within this 0.8% overlapping region suggesting that this level of CYTB distance is the zone where some F1 mammalian offspring begin to require a backcross to generate an F2.
Towards the upper end of distance values between species pairs, both the male and female hybrid offspring of domestic pig (Sus domesticus) × babirusa (Babyrousa celebensis) (12.9%) were shown to be infertile [24]. In addition, controlled, exhaustive efforts failed to produce any viable hybrids between mountain hares and European rabbits (17.3%) [25] (figure 1). The large distance values between these species pairs corroborates previous studies showing that along the continuum of speciation, infertility in both sexes evolves prior to inviability [26–28].
Specifically, distances between domestic cats and jungle cats, leopard cats and servals (7.5%, 10.9% and 11.3%, respectively) are consistent with both the observed minimum (2, 3 and 4, respectively) and average (3, 4 and 5, respectively) number of backcrosses with domestic cats required for hybrid males to acquire fertility [31]. These results are also consistent with an early hybrid experiment using guinea pigs in which hybrids between Cavia fulgida and Cavia porcellus (8.0% CYTB distance) were able to regain male fertility after three generations of backcrossing [32] (electronic supplementary material, table S1).
Our analysis places the distance values between AMH and chimpanzees (11.0%), and AMH and bonobos (10.8%) within category 2, suggesting that even if hybrids could be produced, they would probably follow Haldane's Rule (figure 1; electronic supplementary material, figure S1).
The distance values for all of the pairings of three Homo groups (Sima de los Huesos, Neanderthals and AMH) occupy the bottom of the category 1 range. The distance values for Neanderthals and modern and ancient AMH specifically (1.6%) fall below all the mammalian pairs in this study including polar bears and brown bears (2.4%), and between subspecific crosses of M. musculus (2.3%) (figure 1; electronic supplementary material, figure S1 and table S1). When placed within this context, our data predict that ancient hominin lineages were probably not sufficiently divergent from each other to expect a significant biological impediment to the generation of fertile offspring.
Supplementary material: https://royalsocietypublishing.org/action/downloadSupplement?doi=10.1098%2Frspb.2020.0690&file=rspb20200690supp1.pdf
37874
Some pieces of information:
We first explicitly defined two dichotomous categories along the spectrum of hybrid incompatibility. Category 1 is defined by mammalian species pairs capable of producing fertile F1 offspring of both sexes that can reproduce without backcrossing with a parent species (even if there are observed asymmetries in gene flow and variation in male fertility among the hybrids) (electronic supplementary material, table S1). category 2 is defined by pairs of species that can produce viable F1 offspring, but follow Haldane's Rule, and thus only female F1s can reproduce by backcrossing with a parent species. category 2 also includes species pairs whose hybrids are infertile (electronic supplementary material, table S1).
The category 1 pair with the greatest divergence value was a pair of guinea pig species that were 8.0% divergent, and the category 2 pair with the lowest divergence was a pair of vole species that were 7.2% divergent. Several pairs of species fall within this 0.8% overlapping region suggesting that this level of CYTB distance is the zone where some F1 mammalian offspring begin to require a backcross to generate an F2.
Towards the upper end of distance values between species pairs, both the male and female hybrid offspring of domestic pig (Sus domesticus) × babirusa (Babyrousa celebensis) (12.9%) were shown to be infertile [24]. In addition, controlled, exhaustive efforts failed to produce any viable hybrids between mountain hares and European rabbits (17.3%) [25] (figure 1). The large distance values between these species pairs corroborates previous studies showing that along the continuum of speciation, infertility in both sexes evolves prior to inviability [26–28].
Specifically, distances between domestic cats and jungle cats, leopard cats and servals (7.5%, 10.9% and 11.3%, respectively) are consistent with both the observed minimum (2, 3 and 4, respectively) and average (3, 4 and 5, respectively) number of backcrosses with domestic cats required for hybrid males to acquire fertility [31]. These results are also consistent with an early hybrid experiment using guinea pigs in which hybrids between Cavia fulgida and Cavia porcellus (8.0% CYTB distance) were able to regain male fertility after three generations of backcrossing [32] (electronic supplementary material, table S1).
Our analysis places the distance values between AMH and chimpanzees (11.0%), and AMH and bonobos (10.8%) within category 2, suggesting that even if hybrids could be produced, they would probably follow Haldane's Rule (figure 1; electronic supplementary material, figure S1).
The distance values for all of the pairings of three Homo groups (Sima de los Huesos, Neanderthals and AMH) occupy the bottom of the category 1 range. The distance values for Neanderthals and modern and ancient AMH specifically (1.6%) fall below all the mammalian pairs in this study including polar bears and brown bears (2.4%), and between subspecific crosses of M. musculus (2.3%) (figure 1; electronic supplementary material, figure S1 and table S1). When placed within this context, our data predict that ancient hominin lineages were probably not sufficiently divergent from each other to expect a significant biological impediment to the generation of fertile offspring.
Supplementary material: https://royalsocietypublishing.org/action/downloadSupplement?doi=10.1098%2Frspb.2020.0690&file=rspb20200690supp1.pdf