Firefly "femmes fatales" acquire defensive steroids (lucibufagins) from their firefly prey

Abstract

Female fireflies of the genus Photuris, the so-called firefly "femmes fatales," prey on male fireflies of the genus Photinus. The females are able to entrap the males by faking the flash signal characteristics of the Photinus female. We found that by feeding on Photinus males, Photuris females gain more than nutrients. They also acquire defensive steroidal pyrones called lucibufagins, which are contained in Photinus but which Photuris fireflies are unable to produce on their own. Photuris females that eat Photinus males or lucibufagin are rejected by Phidippus jumping spiders. Lucibufagin itself proved to be a deterrent to such spiders. Field-collected Photuris females contain lucibufagin in varying amounts. The more lucibufagin they contain the more unacceptable they are to Phidippus.

Figure 1

(A) Photuris (versicolor complex). (B) P. ignitus. (C) P. marginellus. (D) Photuris female feeding on a P. ignitus male. (E) Comparable to preceding, later stage of meal. (F) P. audax eating a field-collected Photuris female. (G) P. regius being offered a freshly killed D. melanogaster. (A–C, Bar = 1 mm.)

Figure 2

Photuris female, reflex-bleeding. The beetle had been picked up in forceps, causing it to emit a droplet of blood from the right elytron. Other fireflies, including species of Photinus, reflex-bleed similarly when disturbed.

Figure 3

Body LBG content of field-collected male and female fireflies, plotted as a function of date of collection (Ithaca, NY); n = 10 per column, except where otherwise indicated.

Figure 4

LBG content of Photuris females that ate two P. ignitus males (n = 6) or were kept unfed (controls; n = 15). LBG values are expressed as concentration (in blood and body) and as whole body content. Only 5 of the 15 controls were analyzed for whole body content. In all three cases, differences were significant (t tests, P < 0.01).

Figure 5

LBG content of Photuris females, plotted as a function of LBG-I consumed. Data are presented as concentration and whole body content, as in Fig. 4. In all three cases, significant differences were detected [ANOVAs of log (x + 1) transformed data, P < 0.0001]. Within a plot, columns not sharing underlining are significantly different (experiment-wide α = 0.05).

Figure 6

Predation tests with Phidippus spiders (A and C, P. audax; B, P. regius). (A) Acceptability of Photuris females, plotted as a function of whether or not they had eaten 2 P. ignitus males (n = 29 per category). (B) Acceptability of D. melanogaster, plotted as a function of quantity of LBG-I added topically (n = 20 per category). (C) Acceptability of field-collected female Photuris, plotted as a function of LBG concentration in blood. Acceptability was dependent upon treatment (A and B) or blood LBG content (C) (G-tests, in each case, P < 0.00001).