Decline in predators is causing genetic shift in species
The decline in the Tasmanian devil population is causing a genetic shift in spotted quolls. Researchers have found reduced competition for prey has impacted the muscle development, movement and feeding patterns of the quoll.
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00:00 Well, the study, we took about 300 samples from spotted tail quolls right across their
00:11 range and across the time, a gradient of time since the devil disease emerged in different
00:21 parts of the state.
00:22 So we've got an east-west spread of the disease, therefore an east-west spread of the decline
00:28 of Tasmanian devil populations over a 25-year period.
00:33 And so we sampled the genomics of the quoll across that and discovered some differences
00:42 there.
00:43 It's a really significant study, this, because it's a very new method.
00:48 This is one of the first studies where you've been able to demonstrate changes in the evolutionary
00:56 selection pressure and traits of a species when another species in an ecosystem declines,
01:04 in this case the top predator and top scavenger in Tasmanian ecosystems.
01:10 It's quite incredible, and that is purely because the study, or not purely, but the
01:14 study was done over such a large number of years.
01:18 Yes, well, they're not a common species, so it's taken a long time to get the samples,
01:24 but we can anchor them according to time since the disease outbreak of the devil.
01:30 Yes.
01:31 Okay, so tell us about some of the differences that you found, some of the genetic modifications.
01:38 Well, as the devil has disappeared or declined in the system, we've got genetic changes in
01:46 muscle development and genes, parts of the genome associated with locomotion in quolls,
01:54 and also with their reproduction.
01:57 We're also getting less movement of quolls across the landscape.
02:03 When young quolls leave home, they're weaned from their mother, and they're not moving
02:09 as far.
02:10 That implies that there's more food available in the landscape and less chance of encountering
02:15 a devil.
02:17 Devils compete with quolls in several ways.
02:21 They compete with them for prey, the amount of food in the landscape, but probably more
02:26 importantly, devils are our top scavenger.
02:29 When there's devils in the landscape, there's very little carrion, like carcasses of anything
02:34 left, because the devils clean them up.
02:36 We have shown behaviorally that quolls are eating a lot more carrion when devils disappear,
02:43 but now we can show that that actually changes the amount of food available for quolls, and
02:50 it's changing their locomotion, and it's changing their movement across the state.
02:55 Have you come to a conclusion as to whether it's changing it for the better or not?
03:02 I don't think that's really an important question, because systems are dynamic.
03:11 This actually builds on some work that I did about 30 years ago, where I showed that 3,000
03:17 years ago, when the devil and the thylacine became extinct on the mainland, the tooth
03:23 size and tooth structure and jaw strength of the quoll species changed on the mainland,
03:30 so it relaxed.
03:32 Quolls were actually eating a wider spread of prey sizes relative to Tasmania, where
03:38 you still had devils and thylacines.
03:40 This is our second time that we've been able to establish a clear causation of competition
03:52 actually structuring the morphology and the traits of a species in a community, a wild
03:59 community.
04:00 Really interesting.
04:01 Okay, so the Tasmanian devil numbers had an impact on the quolls.
04:06 I wonder if the quolls' changes in behaviour impacts other species as well.
04:11 This presumably has knock-on effects.
04:13 I'm sure that it does.
04:16 This is actually the first of about five species that we'll be examining in this Guild.
04:23 Where the devil has declined, it's resulted in a shuffle in species abundances right through
04:31 the food web, and we're going to also be looking at some of those other species.
04:36 But I don't think this result really has a conservation implication for quolls.
04:41 It does mean that things are quite good for quolls at the moment, but if devils recover
04:46 from the disease in the future, which is likely because the disease has now reached replacement,
04:54 it's now an endemic disease.
04:56 So if devil populations recover, then the evolutionary selection on quolls will change
05:02 back to what it was.
05:03 Does that make sense?
05:06 Yeah, no, I absolutely get that.
05:07 It makes complete sense.
05:10 Where does your research go from here then?
05:13 Well, we're now examining other species in the mammal community in Tasmania, and we're
05:22 just incrementally building up a picture of how devil decline changes other species.
05:29 Probably of concern is that devil decline results in an increase in feral cats in the
05:33 landscape.
05:34 So if devils did recover, then they would then function to suppress cat populations
05:40 again.
05:41 And that's good because as cats have increased, we're losing things like bandicoots and eastern
05:47 quolls and a lot of our small mammals.
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