1. Evidence for overland dispersal in a flightless aquatic insect
Kate Boersma and David Lytle
Oregon State University

2. Research Goals
To examine the potential for overland dispersal in a flightless aquatic invertebrate top predator
To identify the relationship between dispersal capacity and the conservation of a threatened species
Photo: Alex Wild

3. Why is dispersal important?
Gene flow between populations
Buffer against environmental change
Recolonization
Metapopulation dynamics

4. Why is dispersal important?
Gene flow between populations
Buffer against environmental change
Recolonization
Metapopulation dynamics

5. Why is dispersal important?
Gene flow between populations
Buffer against environmental change
Recolonization
Metapopulation dynamics

6. Why is dispersal important?
Gene flow between populations
Buffer against environmental change
Recolonization
Metapopulation dynamics

7. Why is dispersal important?
Gene flow between populations
Buffer against environmental change
Recolonization
Metapopulation dynamics

8. Madrean Sky Islands
Tucson

9. Arid headwater streams
Fragmented perennial pools
Entire reaches can condense down to one or two refuges
Climate projections suggest further drying in the next 50 years
Grimm et al. 1997; Lake 2003; Barnett et al. 2008

10. Dry season dispersal capacity
Little to no dispersal
Extensive dispersal

11. Dry season dispersal capacity
Little to no dispersal
Extensive dispersal
Fish and some invertebrates

12. Dry season dispersal capacity
Little to no dispersal
Extensive dispersal
Fish and some invertebrates
Aquatic insects with terrestrial adult stage

13. Dry season dispersal capacity
Little to no dispersal
Extensive dispersal
Fish and some invertebrates
Flightless aquatic insects?
Aquatic insects with terrestrial adult stage

14. Abedus herberti 30-45mm An invertebrate top predator
Photo: Mike Bogan
30-45mm
An invertebrate top predator
Flightless, with limited overland dispersal
Sex-role reversed
Obligately aquatic
AIR BREATHER!
Finn et al. 2007; Lytle 2008; Lytle et al. 2008

15. Rationale Avoidance of local extinctions?
Recolonization following extinctions?

16. Evidence for dispersal mtDNA study
Populations more closely related within mountain ranges than within streams
Rare overland dispersal events at evolutionary time scales, measures movement during the last glacial period
Ecological time scale?
Finn, Blouin, Lytle 2007

17. Evidence for dispersal mtDNA study
Populations more closely related within mountain ranges than within streams
Rare overland dispersal events at evolutionary time scales, measures movement during the last glacial period
Ecological time scale?
Finn, Blouin, Lytle 2007

18. Evidence for dispersal mtDNA study
Populations more closely related within mountain ranges than within streams
Rare overland dispersal events at evolutionary time scales, measures movement during the last glacial period
Ecological time scale?
Finn, Blouin, Lytle 2007

19. Research questions
What is the scale of dry season dispersal in Abedus herberti?
Do bugs use pool drying as a dispersal cue?
Does dispersal ability vary with sex or reproductive condition?
Photo: Mike Bogan

20. Methods - Do bugs use pool drying as a dispersal cue?
Bugs start the experiment in an opaque tub inside a larger tank filled with water
Two treatments
1: Dry pool (unfavorable)
2: Wet pool (favorable)
Record movement from the inner to the outer tank relative to treatment
Add info on the scale of movement - small nested tanks are not a realistic approximation of natural interpool distances. But bugs in the inner pool couldn’t see outside. So the decision to leave the inner pool was an appropriate representation of the level of risk involved in dispersal in the field.

21. Methods - Do bugs use pool drying as a dispersal cue?
Bugs start the experiment in an opaque tub inside a larger tank filled with water
Two treatments
1: Dry pool (unfavorable)
2: Wet pool (favorable)
Record movement from the inner to the outer tank relative to treatment
0.61m
Add info on the scale of movement - small nested tanks are not a realistic approximation of natural interpool distances. But bugs in the inner pool couldn’t see outside. So the decision to leave the inner pool was an appropriate representation of the level of risk involved in dispersal in the field.

22. Methods - Do bugs use pool drying as a dispersal cue?
Bugs start the experiment in an opaque tub inside a larger tank filled with water
Two treatments
1: Dry pool (unfavorable)
2: Wet pool (favorable)
Record movement from the inner to the outer tank relative to treatment
0.61m
Add info on the scale of movement - small nested tanks are not a realistic approximation of natural interpool distances. But bugs in the inner pool couldn’t see outside. So the decision to leave the inner pool was an appropriate representation of the level of risk involved in dispersal in the field.

23. Methods - Do bugs use pool drying as a dispersal cue?
Bugs start the experiment in an opaque tub inside a larger tank filled with water
Two treatments
1: Dry pool (unfavorable)
2: Wet pool (favorable)
Record movement from the inner to the outer tank relative to treatment
0.61m
Add info on the scale of movement - small nested tanks are not a realistic approximation of natural interpool distances. But bugs in the inner pool couldn’t see outside. So the decision to leave the inner pool was an appropriate representation of the level of risk involved in dispersal in the field.

25. Methods - Does dispersal ability vary with sex or reproductive condition?
Lab study
Bugs start the experiment in a small pool inside a larger tank filled with water
Apply 2 treatments
1: Dry pool (unfavorable)
2: Wet pool (favorable)
Record movement from the inner to the outer tank and relationship to reproductive condition

26. n=3
n=8
n=12
n=4
n=3

27. Scaling up

28. Evidence for LDD? High Creek video
High Creek, Galiuros, AZ
4.6m/min

29. Evidence for dispersal? Ash Creek recolonization
2000
2003
2009
A. herberti present
A. herberti disappears from Ash Creek
A. herberti absent
Two males present in spring sample
Emphasize that bugs are conspicuous and easy to sample. Found in bathtub-sized pools. These samples were all taken by Mike Bogan - consistent sampling effort. Extremely unlikely that bugs were missed.
Nearest known source population on the other side of the mountain range ~
Bogan unpublished

30. Evidence for dispersal? Mark-recapture study
461 bugs marked; 75% recaptured
81% of recaptures were philopatric
19% of recaptures left their source pool; half were males and half were females
50% of males had eggs while dispersing
Females dispersed ~20m
Males dispersed ~12m
“We detected” or “at least 19% left”
Lytle et al. unpublished

31. Patterns in movement Dry season dispersal exists in this species
Drying is a dispersal cue
The majority are philopatric
Dispersal may be extensive enough to allow for recolonization of extinct pops

32. Patterns in movement Dry season dispersal exists in this species
Drying is a dispersal cue
The majority are philopatric
Dispersal may be extensive enough to allow for recolonization of extinct pops

33. Patterns in movement Dry season dispersal exists in this species
Drying is a dispersal cue
The majority are philopatric
Dispersal may be extensive enough to allow for recolonization of extinct pops

34. Patterns in movement Dry season dispersal exists in this species
Drying is a dispersal cue
The majority are philopatric
Dispersal may be extensive enough to allow for recolonization of extinct pops

35. Patterns in movement Dry season dispersal exists in this species
Drying is a dispersal cue
The majority are philopatric
Dispersal may be extensive enough to allow for recolonization of extinct pops

36. Sex-biased dispersal?
Demands of male brooding may lead to female-biased dispersal
Scant observational data = males
Mark-recapture study = no difference
Behavioral study = no difference

37. Sex-biased dispersal? Sex-role reversed
Scant observational data = males
Mark-recapture study = no difference
Behavioral study = no difference

38. Sex-biased dispersal? Sex-role reversed Observational data = males
Mark-recapture study = no difference
Behavioral study = no difference

39. Future directions
Continue behavioral study on variation in dispersal capacity with reproductive condition
Expand to include: directionality, slope, distance, and rate of water loss
Examine ecological consequences of local top predator extinctions

40. Future directions
Continue behavioral study on variation in dispersal capacity with reproductive condition
Expand to include: directionality, slope, distance and rate of water loss
Examine ecological consequences of local top predator extinctions

41. Future directions
Continue behavioral study on variation in dispersal capacity with reproductive condition
Expand to include: directionality, slope, distance and rate of water loss
Examine ecological consequences of local top predator extinctions

42. Acknowledgements Southwestern Research Station
Marshall Knoderbane
Laura McMullen
Mike Bogan
Southwestern Research Station
National Science Foundation
Sigma Xi Research Grant
American Museum of Nat History Theodore Roosevelt Award
Oregon State University’s Zoology Research Fund
Roberto Munguia
Asako Yamamuro

44. Proportion dispersing from each treatment

45. All reproductive categories disperse
n = 3
n = 12
n = 8
n = 4