Importance of Bees in Environmental Monitoring The obvious utility of bees in pollination of crops...

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

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0.01

0.02

0.03

0.04

0.05

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Hex

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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”.