W11L1 invasion: evolutionary experiment Flashcards
Biological invasion, why is it relevant
- New and different selection pressures on:
> the invasive species
> the invaded community - Must consider evolutionary responses to predict the spread of invasive species and likely outcomes; management implications
- Accidental ‘evolutionary experiments’ can provide new insights into the evolutionary process
Step in biological invasion process
-transport to exotic range
-release or escape into the environment
-spread and cause impact
Impacts of biological invasions
Biodiversity loss
Damage of ecosystem function
Human health (e.g. spread of disease)
Impacts on agriculture (e.g. crop
damage)
Tens of billions of $$ a year
Effect of evolution on the invasive species
Fewer competitors (intra and interspecific)
Fewer predators and parasites
Novel conditions that may not be ideal
Lead to release from native selection pressure and is now under a different selection pressure
Cane toads features that make them good potential invaders:
Prolific breeders - females produce 8 000-35 000 eggs at a time and can breed at least twice a year
Can breed in a wide range of conditions
Fast development - tadpoles hatch in 48 –
72 hours, metamorphose in 17 – 180 days
Relatively short generation time for a
vertebrate - reach sexual maturity at
around 18 months
Relatively long-lived – breed for at least 5
years in the wild; live for at least 15 years in captivity
Current and projected distribution Of cane toad
Dispersed from Queensland to other northern region
-increasing rate of spread at the invasion front
Faster, longer-legged toads at the invasion front
Cane toads with longer hind limbs move further over 3-day periods (r2=0.34) (a),and are in the vanguard of the invasion front
(based on order of arrival at the study
site; r2=0.11) (b). c, Cane toads are relatively long-legged in recent populations, and show a significant decline in relative leg length with time in older populations (r2=0.05). d, The rate at which the toad invasion has
progressed through tropical Australia has
increased substantially since toads were first introduced in 1935 (r2=0.92).
Spatial sorting… Of toad
Summary of toad study
On the expanding range edge, spatial selection on dispersal drives dispersal and reproductive rates up.
This dramatically increases the rate of range advance.
Studying the toad invasion has led to the recognition of an evolutionary process not driven by classical fitness (“spatial sorting”).
Summary of toad study
On the expanding range edge, spatial selection on dispersal drives dispersal and reproductive rates up.
This dramatically increases the rate of range advance.
Studying the toad invasion has led to the recognition of an evolutionary process not driven by classical fitness (“spatial sorting”).
What is character release
Character release: trait change when individuals colonising new environments are released from native-range selection pressures
characteristic of Jackson chameleon
-small founding pop <40
-9-12 month generation time
-give birth up to 30 live young, no parental care
- in Hawaii: no snake, no lizard eating bird
-in Kenya: large amount of predator
-lead to change in maiting signal, in Kenya is less conspicuous due to predator. In Hawaii have brighter color and larger horn, more conspicuous
Hawaiian chameleons have more conspicuous displays
-Hawaiian have higher luminance but similar chromatic contrast during sexual competition
-there is also a luminance contrast when expose to predator in both luminance and contrast
!no change in chromatic contrast with snake
Evolution vs plasticity in chameleon
Could this be due to a founder effect rather than adaptive evolutionary change since introduction?
-A key problem in studies like this is distinguishing evolution from plasticity
-Plasticity can itself evolve and be an adaptive response
-There are almost invariably interaction between genetic and environmental factors, which are difficult to disentangle even with common garden experiments.
