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The Enigmatic Blue Ghost Firefly Phausis reticulata (Coleoptera: Lampyridae): Observations on its Courtship, Mating and Oviposition Behaviors

Raphael De Cock1, Lynn Faust2 and Sara Lewis3 1 Evolutionary Ecology Group, University of Antwerp, Antwerp, Belgium 2 11828 Couch Mill Road, Knoxville, Tennessee, USA 3 Department of Biology, Tufts University, Medford, Massachusetts, USA

De Cock R., Faust L. & Lewis S. 2014. Courtship and mating in Phausis reticulata (Coleoptera: Lampyridae): male flight behaviors, female glow displays, and male attraction to light traps.

Florida Entomologist 97(4) in press.

Photo: Hugh Faust

Introduction

• Distribution: especially in forested regions of southern Appalachian Mountains, small populations as far west as Texas and Oklahoma

Introduction


TEXAS

OKLAHOMA

Introduction


• Habitat: generally in moist forested habitats with small streams or wetlands nearby, and soils overlain by a thick layer of leaf litter

Introduction


• Habitat: generally in moist forested habitats with small streams or wetlands nearby, and soils overlain by a thick layer of leaf litter

• Phenology - Peak mating season: “early season” (Apr-May ) “late season” (Jun-Jul)

Photo: Hugh Faust

Introduction

• Behavior: males of Phausis reticulata (Say) glow as they fly slowly over the forest floor

Introduction • Large numbers of these low-flying males create

remarkable and eerie display: this gave them their often heard local nickname: “Blue Ghost Firefly”

Photo: Blue Ghost Fireflies, by Spencer Black, North Carolina- NatGeo

Introduction • Recently, displays have become increasingly popular

as ecotourist attractions

Photo: Blue Ghost Fireflies, by Spencer Black, North Carolina- NatGeo

Introduction

• Male Phausis reticulata

Introduction

• Males of Phausis reticulata Say glow as they fly slowly over the forest floor searching for flightless females that are likewise bioluminescent

• strong sexual dimorphism:

♂: normal wings, fly ↔ ♀: neotenic, lack both elytra and wings

Introduction

• strong sexual dimorphism: ♂: normal wings, fly ↔ ♀: neotenic , lack elytra and wings • Because of the female’s appearance: “Appalachian glow-

worm”

Introduction

• strong sexual dimorphism: ♂: normal wings, fly ↔ ♀: neotenic, lack elytra and wings • Because of the female’s appearance: “Appalachian glow-

worm” • Females have several spot-like light organs whose glow is

visible ventrally and dorsally through the transparent cuticle

Introduction

• Previous work described – Morphology (Fender 1966), – Geographic distribution (Lloyd 1965, 2004; Frick-Ruppert

& Rosen 2008) – Seasonal and nightly activity patterns (Frick-Ruppert &

Rosen 2008) – Preliminary observations on courtship behaviors (Lloyd

1965 ) and mating (Frick-Ruppert & Rosen 2008)

Introduction

• Previous work described – Morphology (Fender 1966), – Geographic distribution (Lloyd 1965, 2004; Frick-Ruppert &

Rosen 2008) – Seasonal and nightly activity patterns (Frick-Ruppert &



• Surprisingly little work has been done on P. reticulata courtship, mating behavior, oviposition patterns.

Introduction






• Some authors suggest that pheromones might play a role (Lloyd 1965, 1997a, 1997b, 2004; Frick-Ruppert & Rosen 2008),

Introduction






• Some authors suggest that pheromones might play a role (Lloyd 1965, 1997a, 1997b, 2004; Frick-Ruppert & Rosen 2008),

but no extensive experimental proof

Introduction

Aims

Provide additional insight into the reproductive ecology of this enigmatic and rather atypical firefly species:

Aims

Provide additional insight into the reproductive ecology of this enigmatic and rather atypical firefly species: • Study field populations: observations about courtship, copulation,

oviposition behavior

Aims


oviposition behavior • controlled field experiments to investigate courtship signals,

including the relative importance of possible pheromones and bioluminescent glows

Aims


oviposition behavior • controlled field experiments to investigate courtship signals,

including the relative importance of possible pheromones and bioluminescent glows

• Additionally report: – Spectrum of bioluminescence of P. reticulata – variation in female light organ patterns – detailed descriptions of copulation and oviposition – female egg guarding

• Fieldwork 4-19 Jun 2011 and 15-26 Jun 2013 (second mating peak)

• On several locations within Great Smoky Mountains National Park: West side of Burnt Mountain (730 m), near Park Headquarters (475 m), on the north side of Sugarlands Mountain (845 m), NW flank of Mount LeConte (946 m)

General Material & Methods

Nightly flight activity of males

Result

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Males’ reactions to many different types of glow sources: • Attracted to dimly glowing light sources small dots of phosphorescent paint small Betalights or breaklights

• Not to stronger light sources (LEDs, 9V lightbulbs, other firefly flashes)

Male Search Behaviors

Result

Overflying males often circle back to inspect fainter light sources: • flew around 10-15 sec • at ~ 20 cm height • moving in small circles or spirals ~10 to 80 cm in diameter • often “jitterbugging” and “spotlighting” • some eventually drop directly onto or within 2 cm of the

glowing source


Result

Observations on male search behavior and glow lures suggest: • More likely to inspect and land on lures closely

resembling P. reticulata female glow patterns


Result


resembling P. reticulata female glow patterns • No detection or no response to female-like glows beyond

1 m distance


Result


resembling P. reticulata female glow patterns • No detection or no response to female-like glows beyond

1 m distance • Approaches and landings only during peak male activity

(21:45-22:00): later males seem to ignore glow lures


Result

Female Size

Female body size was highly variable, and we found a 3-fold difference in size measured as pronotal area

Female Size

Result

Variation among Phausis reticulata females in the number, size and position of light spots

Female Display

Result

Schematics showing variation and asymmetry in light spot patterns among 14 “late season” female Phausis reticulata observed in Jun 2011 and 2013 from the GSMNP. Small type females 5-6mm (a- c) bear 3 to 4 light organs; Large type females 8-12mm (d-n) show 6 up to 9 lanterns.

Female Display

Result

Schematics showing variation and asymmetry in light spot patterns among 14 “late season” female Phausis reticulata observed in Jun 2011 and 2013 from the GSMNP. Small type females 5-6mm (a- c) bear 3 to 4 light organs; Large type females 8-12mm (d-n) show 6 up to 9 lanterns.

Female Display & Size

Result


Result

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Pearson r = 0.78, p = 0.007

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Pearson r = 0.78, p = 0.007


Result

Q: Are P. reticulata males more strongly attracted to females with a greater number of glow spots?

Male Attraction and N° ♀ Glow Spots

Q: Are P. reticulata males more strongly attracted to females with a greater number of glow spots?

• Field experiments artificial light lures mounted in traps

(Jun 2013) • Data: number of trapped males as an estimate for the

attractiveness of a glow display • N = 12

Method


? <

5 males 20 males (binomial P = 0.002)

Result

<



However possible violation of assumption of independent trials: glows of trapped males attract additional males into traps?

Result

? <



However possible violation of assumption of independent trials: glows of trapped males attract additional males into traps? Re-analysis with more conservative approach considering only catch success per trap

Result

? <



Result

4/12 traps 8/12 traps 33% capture success 66% capture success

? <


<


Result

4/12 traps 8/12 traps 33% capture success 66% capture success (Fisher’s Exact P = 0.2)

? <


? <

Conclusion


Inconclusive though highly suggestive evidence that males prefer displays with more light spots

Courtship Signals: Glows and Pheromones

Q: What is the relative importance of possible pheromones vs. bioluminescent glows ?

• Field experiment (Jun 2013) • Live field-collected P. reticulata females • Compare the number of males attracted to 3 treatments:

Method


3 treatments: 1. GLOW (n=5) : sealed with an airtight transparent cover

Method


3 treatments: 1. GLOW (n=5) : sealed with an airtight transparent cover 2. GLOW + PHEROMONE (n=6) : mesh cover allowing female’s glow and possible sex pheromones to disperse (closest to natural condition)

Method


3 treatments: 1. GLOW (n=5) : sealed with an airtight transparent cover 2. GLOW + PHEROMONE (n=6) : mesh cover allowing female’s glow and possible sex pheromones to disperse (closest to natural condition) 3. PHEROMONE (n=7) : mesh cover allowing any possible sex pheromones + cardboard shield preventing males from seeing female’s glow

Method


Comparison females’ success in attracting males (landed yes/no): PHEROMONE (n=7): 57% GLOW (n=5): 60% GLOW+PHEROMONE (n=6): 100%

Result


Comparison females’ success in attracting males (landed yes/no): PHEROMONE (n=7): 57% GLOW (n=5): 60% GLOW+PHEROMONE (n=6): 100% Freeman-Halton exact two-tailed p = 0.2

Result


Proportion of overflying males that landed directly on or within 1 m of females (mean + 1 SE)

Result


Proportion of overflying males that landed directly on or within 1 m of females (mean + 1 SE)

Result


Two-way ANOVA: NS

Bioluminescence Emission Spectrum

P. reticulata emission spectrum maximum wavelength male = 552 nm; female max. wavelength = 547 nm.

Result

Bioluminescence Emission Spectrum

Mating

VIDEO mating behavior

Result

Mating

• Mean copulation duration (± SE) : 7.9 ± 1.3 min (n = 5)

Result

Mating


• Small females (<6mm, 4 or less glow spots) were ignored even after antennal contact !

Result

Mating


• Small females (<6mm, 4 or less glow spots) were ignored even after antennal contact !

• Females polyandrous: mated females show typical glow display on subsequent nights and remate with new males in captivity

Result

Mating

Oviposition Behaviors

After ovipositing, females (n = 4) curl their bodies tightly around their eggs, using one or more legs to grasp them.

Result

Oviposition Behaviors

Conclusions

Conclusions

New insights into the courtship signals and mating behavior

Conclusions

New insights into the courtship signals and mating behavior • Phausis reticulata obstacle-filled habitats with dense

understory: may favor evolution of mixed signaling systems that use a combination of pheromones (long-range attraction) and bioluminescence (short-range localization)

Conclusions

New insights into the courtship signals and mating behavior • Phausis reticulata obstacle-filled habitats with dense

understory: may favor evolution of mixed signaling systems that use a combination of pheromones (long-range attraction) and bioluminescence (short-range localization)

• Our experiments provide additional suggestive, though inconclusive, evidence that female-produced pheromones may play a role in P. reticulata courtship

Conclusions

Signaling system much more complex than previously thought: • Begin flight activity: primarily focus on female light

signals ?

Conclusions

Signaling system much more complex than previously thought: • Begin flight activity: primarily focus on female light

signals ? • Later perhaps switching to pheromones at lower

densities of unmated females (pheromone plumes more distinct OR unmated females might release pheromone only later at night) ?

Conclusions Novel evidence that P. reticulata males could use female courtship glows as an honest signal of female reproductive potential: • Across many insects, female body size is correlated with

fecundity


fecundity • Extensive variation in P. reticulata female body size


fecundity • Extensive variation in P. reticulata female body size • Size positively correlated with number light spots in female

glow display



glow display • Suggestive evidence from glow lure experiments that males

prefer displays with more light spots



glow display • Suggestive evidence from glow lure experiments that males

prefer displays with more light spots • overall brightness or glow spot pattern that plays a role ?

New research questions • Need for more detailed research on complex mixed

signaling strategies in this and other glow-worm fireflies



• Characterize pheromones + examine possible effects of female age, mating status, environmental conditions




• Single species or a complex of several species or subspecies? 2 seasonal peaks + occurrence of ignored small 4-spotted vs. larger females with >6 glow spots





• Function of male glow ?





• Function of male glow ? - Hypothesis: male glow triggers female glow = not

supported

Thanks for listening

… any questions?

Acknowledgments

We thank the organisors of the 2014 International Firefly Symposium to offer this chance to share our results. Becky Nichols and Adriean Mayor of the GSMNP for guidance, help and assistance. Raphael De Cock was funded in 2011 by a research grant from the Research Foundation Flanders (F.W.O. file K2.064.11N) and thanks Erik Matthysen for support and advice. We thank Patti Edwards, Kathrin Stanger-Hall and Sarah Sander for their enthusiastic company, assistance and support during 2011 field trips, Henri Tellegen of OceanOptics Inc. for advice on spectrophotometry, Tristan Mooij (Betalight b.v., The Netherlands) for providing information and solutions with Betalights. Special thanks to Zach Kobrinsky and David Liittschwager, on assignment for National Geographic Magazine for housing and help in 2013. This study was performed with the necessary permits (Permit numbers: GRSM-2011-sci-0017, GRSM-2013-sci-0096).

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