I thought I’d share with you something really interesting my father pointed out to me in the front yard a month or so ago. He’s a photography enthusiast and loves his bird watching and noticed a pair of juvenile hybrid lorikeets. Both of the juveniles were expressing phenotypic traits belonging to both rainbow and scaly-breasted species of lorikeets.
Juvenile hybrid lorikeets -
I was blown away, it’s not often you see an example of hybridisation between two distinct species, also known as interspecific hybridisation (http://en.wikipedia.org/wiki/Hybrid_(biology)), in your back yard. What made things even more interesting for me, though thinking about it it’s not that much of a surprise, was the fact that when the parents showed up to feed their offspring they too appeared to be hybrids.
Parents and juveniles -
At the bottom of the photo you can see a parent, which has mainly rainbow lorikeet phenotypic traits but when compared with a pure rainbow lorikeet it doesn’t look the same, it has a lighter coloured chest suggesting it is a hybrid. However, the phenotypic traits don’t look as homogenised, or mixed together, as in their juveniles in the photo, which could suggest that the parents of this adult were both pure.
Rainbow lorikeet (Trichoglossus haematodus) -
Scaly-breasted lorikeet (Trichoglossus chlorolepidotus) -
Specifics behind the speciation between these species of lorikeets doesn’t seem to have been studied in fine detail yet, at least after a quick look through Google Scholar. However, as an evolutionary geneticist currently studying mechanisms of speciation in an Australian lizard, Varanus varius, I would suggest it probably occurred within the last 2 million years in the Pliocene/Pleistocene periods (the same pattern has been documented for the occurrance of speciation in many australian species, birds, reptiles, mammals, insects, etc). During these periods there was a great deal of fluctuation in the climate of Australia, and the rest of the world for that matter. Cyclical ice ages occurred causing contraction of species’ distributions during glacial maxima and subsequent expansions during inter-glacial periods. The ancestral species of lorikeet would’ve been separated into two groups that were genetically isolated from one another for sufficient time that they became separate and distinct species. Eventually, once the climate became more stable, both the species would’ve expanded their respective distributions, over much of the east coast of Australia as is the case. In many areas the distribution of both species overlaps, where they are living together in the same environment. For the most part, sexual selection within each species will mean that males and females will be attracted to the opposite sex of their own species, though sometimes accidents can happen. Maybe during sunset, in the branches of a gumtree mr. rainbow lorikeet notices who he thinks is a beautiful mrs rainbow lorikeet sitting on a nearby branch. However, the light is fading and his eyesight isn’t as sharp as it is usually, and neither is hers, thinking she’s found mr right scaly-breasted lorikeet. With Barry White playing in the background they pair get down to business, only realising the unfortunate mistake they’ve made when the sun rises the next day. But it’s too late, they have to finish what they’ve started and raise the miraculously fertilized eggs.
It’s obvious that this doesn’t happen that often, as rainbow and scaly-breasted lorikeets, though their distributions greatly overlap, still remain two distinct and widespread species. If there was no sexual selection occurring within either species, the two species would just homogenise back into one over time. This is called reticulate evolution, “evolution (cladogenisis) characterized by occasional hybridization and combination of two species.”
Reticulate evolution -
It would be really interesting to keep track of the individuals in this family of lorikeets and follow their subsequent matings. Many questions arise such as: would the hybrid juvenile offspring specifically search for other hybrid offspring, or select either rainbow or scaly-breasted lorikeet mates with no preference, or maybe a skewed preference towards one species over the other? It would give some really interesting insights into sexual selection within and between two different species at a hybrid zone. I’ll have to do a more exhaustive search of the literature as I’m sure a great deal has already been done in this area, on other species elsewhere. Anyway just thought I’d share that little back yard biological gem with you.
Hybrid zones in Australian birds – J. Ford
Speciation, hybrid zones and phylogeography – G. M. Hewitt
Hybrid zones and homogamy in Australian frogs – M. J. Littlejohn & G. F. Watson