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

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

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

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

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

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

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

Madrean Sky Islands Tucson

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

Dry season dispersal capacity Little to no dispersal Extensive dispersal

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

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

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

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

Rationale Avoidance of local extinctions? Recolonization following extinctions?

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

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

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

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

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.

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.

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.

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.

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

n=3 n=8 n=12 n=4 n=3

Scaling up

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Proportion dispersing from each treatment

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