It has been documented in some studies that in an aquatic habitat like a lake or reservoir, despite the presence of many tilapia species, some species of tilapia are more likely to hybridize with each other than with some others. For instance Tilapia guineensis and T.zilli when present have the higher likelihood of forming hybridized forms.
There are a few things to think about here: from looking at the phylogeny it appears T. guineensis and T. zilli are closely related (Nagl et al. 2001, MPE - are there any more recent references)?
Thus it would make sense they hybridise more frequently, as closely related species are more likely to hybridise at the homoploid (diploid) level, for a variety of genomic reasons (Paun et al. 2009 for the plant story).
There may be other relevant factors such as mating behaviour, morphology, or chromosome number differences (I don't know enough about Tilapia to hypothesise about these...)
Dear reasearcher, [in Shirak A et al (2011). Gender and reproductive activity modulate the composition of serum lipocalins in Nile tilapia (Oreochromis niloticus). Gene 504(1): 22-30.], we hypothesized that strength of reproductive barrier between tilapia species is depended on affinity of their (in most male) reproductive pheromones (proteins of lipocalin family) to (female) olfactory receptors.
@ Andrey, from research works, not only was T. guineensis more likely to hybridize with T. zilli,the degree or incidence of hybridization differed across different fresh water environments. What could be the likely cause? does it mean that the reproductive barrier via the interaction of the reproductive pheromones are environment modulated?
Similar observations were also made for Oreochromis niloticus and Sarotherodon galilaeus in both fresh water and brackish environments does the same hypothesis of pheromone receptivity or phylogenetic ancestry apply or something else could be the reason?
Species were defined by human being. Why they mate with each other, then were call hybrid? It is also nominated by human. Different colors of people mate with each other, we also call their offsprings hybrid. What's the difference?
From the point of research, maybe long time ago, they are the same. So there is no hybrid. At some time, they formed their own features. But they also keep their "hybrid" habit.
In commercial ponds O.aureus males and O.niloticus females reproduced with efficiency of 5-15% relative to males and females of the same species. F1 hybrids reproduced with 100% efficiency with both purebred species. I believe that absence of complementary gender, external pheromones and their analogs can lead to hybridization.
@ Andrey could you please highlight the point on complementary gender and external pheromones and analogs as regards hybridization, i would appreciate some insight into the subject. Thanks
Could there be a relationship between availability of complementary gender pheromones and the ability or inability to display pre-mating behavioural isolation?
On going studies with on some group of tilapiine cichlids are pointing to the fact that species are less likely to hybridize when the cephalic morphology are significantly distinct i.. in terms of proportionate features relative to the size of the head.
Is food availability and the presence of unexplored niches a possible cause of hybridization in these species?
It depends how people understand the speciation, and the real status of speciation. Speciation is a gradually process. Two from one undergoes a long period. Specifically, the two undergoing speciation are possible to mate with each other without any incompatibility. Please refer a book: Centrarchid Fishes Diversity, Biology and Conservation, and some other papers about speciation.
From another point of view, male-male competition may drive the male to cuckolder with female from another species. Reference such as: Alternative male reproductive tactics drive asymmetrical hybridization between sunfishes.
its true that ecological, physiological, and sexual selection forces may contribute to this hybridization in species but i'm looking for scenarios specific for tilapia or members of the family cichlidae
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