importance of bees in environmental monitoring the obvious utility of bees in pollination of crops...
TRANSCRIPT
Importance of Bees in Environmental Monitoring
The obvious utility of bees in pollination of crops and wild plants is obvious and generally well understood (at least by those of us here).
The potential of bees for environmental monitoring is less well understood and this is what I wish to try to explain.
Sex and death in bees
The take home message is: the unusual sex determining mechanism of bees renders them more susceptible to extinction than almost all other organisms.
Haplodiploidy results in healthy haploid males and healthy diploid females, but sterile, inviable or triploid offspring producing diploid males.
This is because sex in bees is determined by genotype at a single gene locus.
DIPLOID MALES:result from homozygosity at the sex locus
(Ai Aj) (Aj)
X
Fertilized Egg Unfertilized Egg
50% - (Ai)
50% - (Aj)
50% - (Ai Aj)
50% - 2N (Aj Aj)
And are attempts at female production
Diploid malesInviable
1. Increase female mortality: because fertilized eggs are
normally female
Sterile
1. Increase female mortality. 2. Waste reproductive
opportunities of mates
Diploid Males: two categories
Colletes inaequalis
Diploid Males and Extinction
Large populations have many sex alleles and low diploid male frequencies.
Small populations have few sex alleles and high levels of diploid male production.
Small populations will therefore enter a special case of the extinction vortex.
The Diploid Male Vortex
Probability of extinction in haplodiploid populations with and without DMP
NO DMP DMP w/Inviable Diploid
Males
DMP w/Sterile Diploid
Males
Zayed and Packer 2005
Genetically-induced extinction risk comes from more than diploidy at the sex locus – the genetic load is associated with lethal and deleterious alleles. Haplodiploids are though to have less of this.
DMP versus inbreeding depression in diploids Genetic load in a survey of threatened
diploid animals accounted for an average increase in P(E) of 9.9% over ecological factors (Brooks et al 2002)
When haplodiploid populations with similar sizes and growth parameters were modeled, DMP contributed to an average increase in P(E) by– 52.7% - with inviable diploid males– 63.2% - with effectively sterile diploid males
Bees
Found in almost every terrestrial ecosystem. Numerous guilds can be considered among
the bees, some of these are:– Specialist/generalist floral hosts– Below ground/above ground nesting– Solitary/social– Nesting/cleptoparasitic
Are some of these likely to be more useful than others?
Yes: Bee traits as indicators of ecosystem health
Specialist/generalist floral hosts
Below ground/above ground nesting
Solitary/social
Nesting/cleptoparasitic
Oligolectic bees
Colletinae
Specialists have less heterozygosity than related generalist species
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
Hex
p
Diphaglossine Colletine Panurgine Megachilid Centris
Caupolicana ruficollis on Loasa tricolor Nolanomelissa toroi on Nolana
Centris mixta on Prosopis tamarugales
Packer et al.,2005Hexp
Bumble bees, as social bees, are also expected to be at high risk
Bombus affinis: a species that may be extinct soon.
Courtesy: Sheila Colla
Cleptoparasitic bee species with a single host bee: Epeolus bifasciatus has a
single host species – Colletes latitarsis which is a floral specialists on Physalis
Images by T’ai Roulston
FINAL TAKE HOME MESSAGE Not only are bees important, they (with
other haplodiploids) are likely to be excellent indicators of terrestrial “ecosystem health”.