I know this is a diversion from the original and not about birds, but it
is about the birds and the bees and of course many of you know this but some
won't and may be interested. I was going to type out what is the most
interesting thing about this order of insects but then thought I could save
myself some time by copying the Wikipedia entry on haplodiploidy (with minor
edits and additions from me). I will admit it taught me something. For 39 years
I thought is was a system unique to the insect order Hymenoptera (bees, ants, and wasps), but it appears not,
although it is characteristic of them and important to their social life. It
does go a long way towards explaining why these animals are so vigorous in
defence of their colonies.
Haplodiploidy is a sex-determination
system in which males develop
from unfertilized eggs and are haploid, and females develop
from fertilized eggs and are diploid.[1] Haplodiploidy is sometimes called arrhenotoky.
Haplodiploidy
determines the sex in all members of the insect order Hymenoptera (bees, ants, and wasps),[2]p408 Coccidae,[3] and the Thysanoptera ('thrips').[4] The system also occurs sporadically in
some spider
mites, Hemiptera, Coleoptera (bark
beetles), and rotifers.
In
this system, sex is determined by the number of sets of chromosomes an individual receives. An offspring
formed from the union of a sperm and an egg and is
diploid (two) it develops as a female, and an unfertilized egg
develops as a male. This means that the
males have half the number of chromosomes that a female has, and are haploid.
The
haplodiploid sex-determination system has these peculiarities. A male has no father and cannot have sons, but
he has a grandfather and can have grandsons
(obviously only by inheritance from his mother or daughter) .
Additionally, if a eusocial-insect colony has
only one queen, and she has only mated once
(which is the common system), then the relatedness between all the workers (diploid females) in a hive or
nest is 0.75. This means the workers in such monogamous single-queen colonies
are significantly more closely related than in other sex determination systems
where the relatedness of siblings is usually no more than 0.5. It is this point
which drives the kin
selection theory of how
eusociality evolved.[2]:465 Whether
haplodiploidy did in fact pave the way for the evolution of eusociality is still
a matter of
debate.[5][6] The chromosomes of workers and queens are the same, it
is the feeding of the larvae by their older sisters, believed to be under
instruction from their mother, that sets whether they become workers
or queens.
Another
feature of the haplodiploidy system is that recessive lethal and
deleterious alleles will be
removed from the population rapidly because they will automatically be expressed
in the males (dominant lethal and deleterious alleles are removed from the
population every time they arise, as they kill any individual they arise
in).[4]
Haplodiploidy
is not the same thing as an XO
sex-determination system. In Haplodiploidy, males receive one half of the
chromosomes that female receive, including autosomes. In an XO
sex-determination system, males and females receive an equal number of
autosomes, but when it comes to sex chromosomes, females will receive two X
chromosomes while males will receive only a single X
chromosome.
Also
this other reference that tells a similar story somewhat better which I am
pasting below without any edits from me:
Haplodiploidy
Hymenoptera,
the Order of insects that includes the bees, ants and wasps, has an interesting
and unusual genetic method of sex determination. Males are haploid--they have
only one copy of each chromosome--while females are diploid--two copies of each
chromosome. Female Hymenoptera come about in the usual way, with a sperm from a
male fertilizing a female's egg. One set of chromosomes comes from the father,
the other from the mother, yielding a diploid daughter.
Males,
on the other hand, have a mother but no father. Males develop from an
unfertilized egg, making them haploid. A female hymnopteran can have
sons even if she never mates. Sex determination of this sort--haploid males and
diploid females--is called haplodiploidy. Some
other kinds of animals have the same sort of method of sex determination, but it
is best studied in Hymenoptera.
Gender
is actually determined by a single gene (at least in bees, in which this is well
explored) (Beye et al. 2003). If there is only one copy of the gene, because the
animal is haploid, then the animal develops as a male. If there are two copies
(representing two chromosomes) and they differ in their DNA sequences, then the
animal is female. In other words, an animal that is heterozygous for the sex
determination gene is a female. A homozygous diploid animal develops as a
sterile male. In honey bees the homozygous diploids are killed as larvae,
representing considerable waste to the colony. This means that inbreeding in the
Hymenoptera is costly, and most Hymenoptera avoid inbreeding.
Beyond
this intriguing mechanism, haplodiploidy has important consequences that seem to
affect social behavior:
- If a queen mates only once, her daughters are highly related to each other
(called supersisters), because the father's sperm are all identical.
- A female is more related to her sisters (on average, 75% similar) than she
is to her own daughters (on average 50% similar).
- A female is more related to her son (50 % similar) than she is to a
brother (on average, 25% similar).
These
three factors combine to create a condition in which it may be more
advantageous, evolutionarily speaking, for a female to help her mother produce
sisters (to the female in question) than to produce her own daughters. Thus
haplodiploidy opens the way for the evolution of a worker caste, devoted to
helping their mother. If workers evolve under these conditions, then we would
expect:
- That all workers will be female (males have no special pattern of
relatedness in a haplodiploid system that would make working advantageous to
them
- That workers will help their mother to lay and rear females, but
- That workers would prefer to lay their own male offspring, rather than
rear brothers
In
fact, Hymenoptera workers are uniformly female and conflict between the queen
and the workers over who lays the males eggs in a nest is common. The role of
haplodiploidy in the evolution of worker Hymenoptera fits into an overall theory
of how genetic similarity affects social behavior called kin
selection which was developed
by W. D. Hamilton.
Beye
M, Hasselmann M, Fondrk MK, Page RE, Omholt SW 2003 The gene csd is the primary
signal for sexual development in the honeybee and encodes an SR-type protein.
CELL 114 (4): 419-429
Hamilton
W. D. 1964 The evolution of social behavior I. J Theor Biol 7:1-16
Hamilton W. D. 1964 The evolution
of social behavior II. J Theor Biol 7:17-52.
Philip
All
ants are related to bees and wasps at the level of “order” and the sting of all
ants is in the tail as far as I can see.
David
From: Margaret
Leggoe [
Sent: Saturday, 13 December
2014 2:24 PM
To: Mark Clayton
Cc: Matthew Willis;
CanberraBirds
Subject: Re: [canberrabirds] Birding/Outdoor Tip for the
Day
Bull ants, apparently, are related to wasps and have a sting
in the tail. So it depends on which end of the ant attacks you, how severe the
bite. The sting in the tail is the one to be feared.
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