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[A1CR]

We may be food-deprived, as was the dragonfly-like insect
http://en.wikipedia.org/wiki/Damselfly for which neither
type of fly were in
our archives previously. This, in combination with the
immune risks, may
predispose mortality risk?


Robb T, Forbes MR.
Age-dependent induction of immunity and subsequent survival
costs in males
and females of a temperate damselfly.
BMC Ecol. 2006 Nov 7;6(1):15
PMID: 17090312

ABSTRACT: BACKGROUND: To understand variation in resistance
to parasites
within host populations, researchers have examined
conditions under which
immunity is induced and/or is costly. Both host sex and age
have been found
to influence immune expression and are expected to influence
the costs of
resistance. The purpose of this study was to examine immune
expression and
associated survival costs for two age groups (newly emerged
and sexually
mature individuals) of the damselfly, Enallagma boreale Selys.

Survival was assessed for experimentally challenged and
control damselflies,
housed initially at 22 degreesC and then subjected to low
temperatures (15
degreesC) associated with reduced foraging activity and food
deprivation.
Experimental conditions emulated natural local variation in
bouts of good
weather followed by inclement weather (successions of days
with hourly mean
temperatures around 15 degreesC and/or rainy weather).

RESULTS: At least one of three immune traits was induced to
higher levels
for both newly emerged and mature E. boreale challenged by
Lippopolysaccharide (LPS) relative to saline-injected
controls, when housed
at 22 degreesC. The immune traits assayed included haemocyte
concentration,
Phenoloxidase activity and antibacterial activity and their
induction varied
among ages and between males and females. For matures, those
injected with
LPS had lowered survivorship compared to saline-injected
controls that were
housed initially at 22 degreesC and subsequently at 15
degreesC. Newly
emerged LPS-injected damselflies did not show reduced
survivorship relative
to newly-emerged controls, despite showing immune induction.

CONCLUSIONS: Reduced longevity following induction of
immunity was observed
for reproductively mature damselflies, but not for newly
emerged
damselflies. Costs of resistance depend only partly on the
immune trait
induced and more on the age (but not sex) of the host. In
four years, we
often observed bouts of inclement weather following good
days and these
bouts occurred primarily during the emergence periods, but
also during the
flight periods, of E. boreale. The duration of these bouts
appear sufficient
to compromise survival of mature damselflies that responded
immunologically
to LPS challenge. We further suggest the environmental
conditions likely
experienced by different ages of damselflies, following
resistance
expression, has influenced optimal immune investment by
individuals in
different age classes and the likelihood of detecting costs
of resistance.

Table 1. A summary of the significant results from the
immune trait assays
and the survivorship experiment. See text and Figures 1-4
for exact values
and statistical tests.
=====================================================
Newly emerged Mature
=====================================================
Immune trait assayed
Haemocyte concentration NS LPS > saline
MI LPS > saline females > males
Antibacterial activity LPS > saline^1 females > males
Survival females > males LPS < saline
females > males^2
=====================================================
1 Sex by treatment interaction only females showed
induction of
antibacterial activity with LPS injection.
2 p=0.06

Table 2. Means±1 SE of mass, wing length and median number
of mites on
newly emerged and mature Enallagma boreale for saline
injected and LPS
injected groups used in the survivorship experiment.
============================================================
Mass (g)^1---Wing Length---(mm)^1 Mites^2
Saline LPS---Saline LPS---Saline LPS
============================================================
Newly emerged
Males 0.328±0.007 0.324±0.007 12.87±0.15 12.91±0.11
7 (3-10) 4
(3-11)
Females 0.350±0.008 0.345±0.008 13.81±0.15
13.64±0.16 4 (2-10) 5
(1-12)
Mature
Males 0.304±0.007 0.313±0.007 13.07±0.11 13.14±0.09
0 (0-0) 0 (0-0)
Females 0.464±0.014 0.469±0.010 13.79±0.12
13.74±0.13 0 (0-0) 0
(0-0)
============================================================
1 No differences in mass or wing length were found
between treatment
groups within each age and sex category (Newly Emerged:
Mass- males, t40
= -1.52, p = 0.14; females, t48 = -1.53, p = 0.13; Wing
length- males, t40 =
0.27, p = 0.79; females, t48 = 0.83, p = 0.41; Mature: Mass-
males, t57
= -0.91, p = 0.36; females, t59 = -0.44, p = 0.66; Wing
length-males, t57
= -0.50, p = 0.62; females, t59 = 0.31, p = 0.76).
2 No differences between the median number of parasitic
water mites
(interquartile ranges are indicated in brackets) were found
for saline
injected and LPS injected newly emerged E. boreale (zeros
were included in
analyses; males, W = 161, p = 0.16; females, W = 275.5, p =
0.63). Few (8)
mature adults were found with mites and therefore no
statistical tests were
completed, although medians and interquartile ranges are
reported. Two
males that were saline-injected carried 2 and 27 mites,
three males that
were LPS-injected carried 4, 5 and 15 mites. One female
that was
saline-injected carried three mites and two LPS-injected
females carried one
and two mites.