By Alexandra Salvador
Storified by Alie Salvador ·
Wed, Nov 16 2016 03:08:13
The domestication of today’s chickens can be traced back to their closest wild ancestor, the Red Jungle Fowl, but they could also possibly be interbred/evolved along with the Gray Jungle Fowl and possibly two other jungle fowl species. There is much speculation about when the chicken actually evolved but it’s generally accepted that it was domesticated for cock fighting around seven to ten thousand years ago. Wild red jungle fowl came from the Southeast Asia region and sprawled out to the rest of the world from there. It’s likely there were more than one events of domestication of some type of jungle fowl (Adler 2012). One author pointed out that this bird which has no flight or migration, can only hop up a few feet at a time, doesn’t run very fast, and has no swimming ability has successfully reached all corners of the world from it’s origin in jungle regions of Southeastern Asia. This amazing span achieved by the chicken can be attributed to human transportation of the species (Storey et. al. 2012). In fact, the routs which chickens were transported can tell a lot about human history since the chicken has significant cultural, religious, and dietary significance (Storey et al. 2012) Turns out I’m actually not the first one to write a paper looking at the evolutionary history of what we today call a chicken. Actually, the first person who did was Ulisse Aldrovandi in 1600 A.D. Rome his work was about the history and varieties of domestic chickens. This only goes to show how pervasive and evolutionarily successful this animal has become.
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It’s often cited that the chicken’s closest relatives are the Red Junglefowl but it’s just not that simple. Animals breed with whatever other animals they’re around in order to continue their species (humans are of course no different). So through trade and exchange of the bird it cross bred with many types of wild junglefowl and other domesticated chickens. This affects the lineage of the chicken and their wild counterparts. Note that when I say chicken, thousands of years ago at the time of its domestication, there really wasn’t much different between in and the junglefowl. Domestic chickens were basically domestic junglefowl until breeding and selection for certain traits by humans made the animal truly domestic over decades (Storey et al 2012).
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The map created by the research team led by Alice Storey explains a few things about where chickens were domesticated and when. The dark red area in Southeast Asia is the natural range of the Red Junglefowl (however, there’s debate that they could have ranged further north in prehistoric times). The circles numbers represent where the archeological remains were found and the color suggests the “haplogroups” which are a genetic population stemming from a common ancestor. The dark green and blue haplogroup is a group of DNA sequenced from Thai chicken samples and dates back about 2,500 years. The blue group dates back about 1,600 years, and the pink is about 700 to 550 years ago (Storey et al 2012).
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The chicken has led many historians to believe that there were more than one locations and times when the junglefowl was domesticated. Archeologists identified that chickens were domesticated in India and China within the range of the wild Junglefowl. Even though there is not as much evidence historians and biologists speculate they were most likely also domesticated in Burma, Malaysia, and Thailand (Storey et al. 2012). The earliest recorded chicken remains date back to 5400 B.C. in the Hebei Province of China. Chickens entered mainland America several times but first in A.D. 1500 (Storey et. al. 2012).
The actual habitat the original Red Junglefowl prefer is tropical and subtropical generally using trees and bushes or mangroves as protection and habitat while foraging in open spaces. They generally like to perch in trees but while mothers are with young they nest on the ground. They enjoy pretty flat ground and the edges of forests (Corder 2007). When deciding on which type of habitat would best suit a domestic chicken today, it’s wise to consider the habitat of close evolutionary relatives.
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In trying to deconstruct the evolutionary history of the chicken including its closest relatives from the order Galliformes. I found a very complex phylogenetic analysis by researchers led by Ning Wang of the sister species to Gallus Gallus (Red Junglefowl). The attached chart is what shows the closest relationships between species evolutionarily. They found that the most probable sister species to Gallus gallus was the Gallus varius (Green or Javan Junglefowl native to Indonesian Islands), Gallus lafayetii (Sri Lankan or Ceylon Junglefowl), and Gallus sonneratii (Grey Junglefowl native to India) (Wang 2013). The Gallus gallus domesticus we know today has probably benefited from the genes of all of these wild junglefowl at some point in its evolutionary past. On a broader scale, looking at the linnaean classification system we can see that chickens have developed traits from many different Galliformes including pheasants, partridges, quails, guinea fowl, and turkeys (Wang 2013).
Nicholas E. Collias a well studied ornithologist did research on the vocal repertoire of the red junglefowl and related that to the domestic fowl we have as chickens today. He says the vocal language of the two birds (Wild Junglefowl and Chicken) is almost the same and their signals represent the same moods and emotions. The bird population he studied seemed to be a challenge due to the wild bird being unapproachable so he used a captive example of junglefowl in a zoo setting, this could alter his results. He identified 24 different calls for the Red Junglefowl categorized into chick exclusive calls, adult calls, male rooster calls, and hen calls. What he found was that these birds can generally communicate with the types of noises they make and those noises being associated with different meanings (Collias 1987). For example, a cock that is trying to court a hen will have a specific courtship call, a loud defense call means there’s a nearby threat (Collias 1987).
The chicken uses many types of vocalizations to communicate with the members of its species. In fact vocalizations can begin as early as the embryonic stage within the egg, between hen and egg (Jacob 2015). Though hearing and making noise is mostly how chickens communicate they also communicate with body language a fair amount. For example, when a hen believes her chicks are big enough she pushes them away and rejoins the adult birds (Jacob 2015). Chicks of about 16 days old begin competition to establish dominance known popularly as a “pecking order” in which they establish through literally pecking each other around food sources or sources of heat or just in general. They also show cooperative social behavior in which “leader” birds will cause other birds to follow them to sources of food/heat/shelter. Another example of cooperative behavior is when chickens snuggle together when it gets colder at night (Jacob 2015). When adult birds fight, it’s either because a new bird has entered the flock, a male is challenging another male (for territory or hens) or a bird wants to change its rank in the pecking order. The fights begin when birds raise their neck feathers and points their wings to the ground and away from their body to make themselves look large. They stand tall as they fight which involves jumping, pecking, scratching, and beating each other (Jacob 2015). Generally, in small flocks of chickens or wild junglefowl, males and females have separate pecking orders (Cheng 1988).
The main sensory inputs chickens rely on is their ability to hear and see. Since chickens primarily communicate using vocalizations it’s essential that they be able to hear, and they do very well. Birds, including chickens, don’t look like they have an ear since they only have the canal leading to the eardrum. They also have an amazing sense of sight which is important for foraging, protection, and picking up on other bird’s queues.
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When it comes to Gallus gallus you’ll have to shift your idea of the mammalian reproductive system. Hens (female chickens) have a single ovary, this was an evolutionary development for easier flight. Hens are born with two ovaries but only one actually develops. Male birds or roosters have one teste which is much larger which is the phasing out of the two tested genes. However, the rooster can still reproduce using just the smaller teste (Dickinson 2012). Birds like to be super efficient for flight and even though chickens can’t fly they still have many of the adaptations for flight. Just like a lack of external ear skin they also lack external genitalia. So how does the sperm get into the female bird then? Both male and female chickens have one “hole” the cloaca from which all waste and reproductive products come from. To mate, the male rooster sits on top of the female bird and from his cloaca comes the sperm before going into the female hen’s cloaca (Dickinson 2012). One fertilization will last a hen four weeks of egg laying since she stores the sperm in an internal pouch. Although chickens still lay eggs almost daily even without fertilization, it’s as natural and recurrent as ovulation for mammals (Dickinson 2012).
The behaviors that adult chickens generally show towards each other are: approaching (male walks towards female with head facing her), precopulatory waltzing (the rooster courtship display), crouching (female receptive posture), Mounting attempt (male attempts to get on top of the hen by grabbing her back), treading (male walks in place on female’s back), and tail bending (male bends his tail around the side of the female's tail) (Cheng 1988).
Gallus g. goes about a series of mating behaviors. First the rooster will do his courtship dance (see the video). He drops one wing so the inside will face the hen and dances in a circle around his wing. If the hen likes him she’ll stop foraging and crouch with her wings sort of puffed out and her head down. The rooster hops on her back and grabs the back of her with his beak and begins walking in place on her back then, with his long spurs, latches to her sides. The mating is finalized when the rooster ejaculates into the hen’s cloaca. The whole process happens relatively quickly within a few seconds or minutes (University of Georgia, 2009). A rooster can mate up to 30 times a day depending on the females willing to mate with him, although, sperm concentration decreases as the day goes on (University of Georgia, 2009).
Domestic Gallus gallus uses a polygynandrous mating system. They usually group together in small flocks composed of mostly females, a dominant male, and one or more subordinate males. It’s common in these flocks that the most dominant male mates with the females much more often than the subordinate males (Cheng 1988). In chickens that are allowed to flock like this, it is shown that the hens will mate with both subordinate and dominant males and have chicks with genes from both males, this is called “multiple paternities”. There are four known factors that would determine which bird would be the father and successfully fertilize a hen with his sperm, this is known as paternity. Of course the dominant male will want to “mate guard” and keep other roosters from mixing there genes with his, this is known as “sperm competition” (Cheng 1988). The first factor is the timing and success of different males, then the relative numbers of copulations by different males, the amount of time sperm is stored by the hen, and “sperm precedence”. This particular study analyzed how roosters mate at different times of the day when alone in a flock of females and when competing with subordinate males. They found that the single males (no other roosters) had similar mating patterns (mounting attempts) to the domestic males in the two rooster flock. However, the subordinate males were much less successful in mating. The males had the most attempts in the late afternoon and less in the morning. This is interesting because studies show that female hens are most fertile at certain periods of the day when their egg doesn’t have a hard shell yet which is more present in the morning than the afternoon. Hens are also more receptive during the afternoon. (Cheng 1988). Another interesting finding was that the hens were much more receptive to the single males than either the dominant or subordinate males in the other flock. (Cheng 1988).
The sexual selection of chickens depends on female choice and male dominance. A paper called Female Mate Choice and Male Behaviour in Domestic Fowl by Marty L. Leonard set out to answer the question; “what makes a rooster “attractive” to a hen?”. They tested their hypothesis by examining mate selection by female Gallus gallus domesticus looking at five behavioral and six morphological traits to discover which ones hens queued on most (Leonard 1998). What’s interesting to note about this study is that their results differ from related work on the Red Junglefowl which is the wild ancestor of the domestic chicken. The point of these courtship behaviors from an ecological perspective is that the display of a male helps a female judge his parental abilities, protection abilities, genetic quality, and general attractiveness. What was found in the study on Junglefowl was that females were queuing on comb size when it was larger than a normal male comb. Hens don’t mate randomly they often show preference for dominant males. Chickens in the “wild” and junglefowl live in small social groups made up of one dominant male and several females and occasionally some subordinate males. Females mate most often with the dominant male but also sometimes mate with other males in the group (Leonard 1998). They found that in all of their trials the males with the most “wing flapping” were always preferred. The discussion sections points out that wing flapping occurs during courtship and one other time, aggressive fighting with other males, this could be the reason for preference of more wing flaps. They also point out that sexually active males wing flap more than non-sexually active males, it could be an indicator of viability (Leonard 1998). A previous study also suggests that wing flapping may suggest rank, dominant males flapping more than subordinate males. Similar studies on Red Junglefowl suggest that the hens queued more on morphological traits than courtship actions. These traits were comb size and comb color, the more prominent and red the comb the higher ranking the male, there’s also a positive correlation to good health (Leonard 1998). One possible reason for Junglefowl giving more preference to males with larger combs than domestic chickens could be because domestic chickens have the genes for comb size variation were bred out of the roosters making this not as good of an indicator for domestic birds anymore, that of course is one hypothesis, it could also have been how the study was conducted or that domestic chickens queue on different signals than their wild counterparts (Leonard 1998).
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