The whitetail rut is a frenzied scramble. Literally, that’s the biological term for the whitetail breeding strategy – “scramble competition” – because a buck’s success at breeding does is determined mostly by his ability to search for and find estrus does quickly. After each, he moves on to search for another one. In this rushed scramble, do bucks ever run across their own “daughters”? If so, do they attempt to breed them, and are they ever successful? This was a question I received from Casey Christman, co-host of American Archer on the Outdoor Channel. I didn’t know the answer for certain, so I went to someone who probably would.
Before I share the expert’s view, let’s look at some behaviors that reduce the likelihood of such an encounter from the outset.
There are many fail-safe behaviors built in to prevent deer inbreeding – I mean, we’re talking about a species that has been thriving on this continent for at least 2 million years, so they’re doing something right. The majority of yearling bucks leave their birth range and travel a few miles before setting up their permanent adult home range, a behavior called “dispersal” that flings genetics far from where a buck was born and makes it unlikely that a doe might ever visit the same scrape as her own buck offspring.
Does also disperse as yearlings, but at a lower rate, less than half of them according to Penn State University research. Those that don’t disperse tend to remain with their mothers as part of an extended matriarchal family group of does. So, it’s entirely possible for an adult buck’s home range to overlap the ranges of his own female offspring of breeding age, and the odds climb as he gets older.
They’ve never documented an individual buck that bred the same doe in multiple years, even though both adults lived in the same area.
Dispersal is only the first of many behaviors that prevent cousin coupling. Adult bucks and does with established home ranges take excursions during the rut, or short vacations of a few miles and a few days outside their usual neighborhood, which further scatters deer DNA on the landscape. Then, there is an incredible amount of competition to breed, at least in a population with a natural and balanced ratio of bucks to does. Research has found the average buck successfully sires surprisingly few fawns in his lifetime.
All of this helps prevent inbreeding. If it happens, it would have to be fairly uncommon and therefore have little or no impact on survival fitness in the population. Still, Casey’s question was valid. If all else fails, would close relatives “recognize” the connection somehow and decline the opportunity? Does it ever happen?
Look to Deer DNA
I turned to Dr. Randy DeYoung at Texas A&M-Kingsville’s Caesar Kleberg Wildlife Research Institute, who earned his degrees just as the technology for deer DNA analysis was becoming widely available and feasible. Randy has studied whitetail DNA and family trees more extensively than any researcher I know.
“With so many bucks competing to breed, it may be hard for two close relatives to end up together at the right place and time,” Randy said.
As an example, Randy told me something that surprised me. In all of the Institute’s DNA work looking at buck breeding success, antler trait heritability, and other genetic factors, they’ve never matched a wild buck and doe pair that successfully mated with each other more than once.
Think about that. They’ve never documented an individual buck that bred the same doe in multiple years, even though both adults lived in the same area. Of course, their sampling and studies cannot examine 100% of any wild population, but to never find this in all of their extensive relationship studies suggests it is extremely rare. The biology term “scramble polygyny” is certainly accurate for whitetails (“polygyny” means having more than one mate).
But what about the original question: Bucks breeding their own offspring?
“I don’t recall any instances of mating between known relatives in the work we have done on deer, though we did not always have complete information on who’s related to who,” said Randy. “The ability to recognize relatives and avoid inbreeding is not really known. Other species seem to have at least some ability to avoid close relatives, though this can break down when mating opportunities are limited, such as in small populations or captive settings.”
Randy mentioned an example from the ocelot of South Texas, a small wildcat that is not endangered worldwide but numbers less than 200 animals in the isolated Texas population. In this small local group, the Institute’s long-term work has confirmed parent-offspring mating.
So, we don’t know that it can’t happen in deer. We can’t show that deer recognize relatives when they cross paths at the local licking limb and turn the other direction with a deer’s version of the “Ew” vocalization. But considerable genetic research has yet to confirm it happening. We may never have a definitive answer, but if it occurs, it’s extremely rare.