>Gene expression can be a covariant of size -- greater quantity and
concentration of hormones, passively present in a larger volume. In other
words, nothing definitive about the queen herself controlling the
developmental trajectory of the fertilized egg being deposited.
I would concur that the first two studies present the case whereby larger
eggs are more nutrient-rich which may partially explain the structural
differences between large and small eggs.
But we still have the question of whether the resident queen makes a
decision to lay a larger egg - and if so, why:
A Maternal Effect on Queen Production in Honeybees
<https://www.cell.com/current-biology/fulltext/S0960-9822(19)30673-6?> - Han
et al
This suggests that the gene expression differences between adult queen from
QE and WE are reflective of variation in the caste development process. Our
DEGs contained a disproportionately large number of genes such as juvenile
hormone methyltransferase, abaecin, and hexamerin genes involved in hormone
synthesis, ovary development, cuticle development, and immune functions.
We now recognize, however, that the epigenetically differentiated worker and
queen developmental pathways are sensitive to the early larval environment,
and our data also indicate a sensitivity to the in ovo environment. This
adds a new perspective on colony function and indicates that the queen has a
more active role in the production of the next generation of queens than has
been previously recognized.
Honeybee (Apis mellifera) Maternal Effect Causes Alternation of DNA
Methylation Regulating Queen Development
<https://pdfs.semanticscholar.org/2b4c/ddf1c2ad9dafd21ef46e45541a07c67a5315.
pdf> - He et al
Larger eggs found in queen cells may contain more nutrients than eggs in
worker cells, therefore, the nutrients available to the developing embryo
may alter DNA methylation and promote queen development. However, the kind
of nutrients in the eggs and how queens control egg size requires further
investigations.
How DNA methylation regulating gene expression remains essentially unknown
in honeybees. DNA methylation has been shown to associate with chromosome
structure and histone modifications (Hunt et al., 2013; Dmitrijeva et al.,
2018). Perhaps the alternative splicing, chromosome structure, histone
modification and other undiscovered factors jointly contribute to the
regulation on honeybee gene expression by DNA methylation, which needs
further investigations.
The second two studies appear to suggest a more active role by the resident
queen in choosing not only egg size based on perception of colony status but
also initiating several upregulated egg development processes.
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9146148/> High-Quality Queens
Produce High-Quality Offspring Queens - Yu et al
. we propose that QE larvae may produce more pheromones, and that nurse bees
may perceive the pheromones of larvae and provide larvae in QE queen cells
with more fresh royal jelly.
In our study, we found that the expression of Abaecin, Hymenoptaecin, and
CytP450 in the queens of F2-QE were the highest, suggesting that the
immune-detoxication of offspring was affected by maternal effects, and the
immune-detoxication of queens of F2-QE was superior. We observed that the
queens of F2-QE had the highest newly emerged weight and the highest number
of ovarioles. In summary, the expression level of development-, immune-, and
detoxication-related genes showed a decreasing trend among the three groups
of F2 queens.
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/> The Molecular Basis
of Socially Induced Egg-Size Plasticity in Honey Bees - Han et al
These results elucidate how the social environment of the honey bee colony
may be translated into a specific cellular process to adjust maternal
investment into eggs.
In our first experiment, we found that egg size was negatively correlated to
egg number produced. To test whether small egg size is merely a passive
consequence of high egg-laying rate, we thus assessed egg size before and
after a 2-week period of queen caging, which prevented queens from laying
any eggs. None of the four caged queens significantly changed her egg size
(F(1,38) = 0.02-1.8, all p>0.1). None of the four queens in an unmanipulated
control group during the same time changed her egg size either (F(1,38) =
0.005-0.6, all p>0.4), and egg sizes were similar between the restricted and
unrestricted groups overall.
To better understand how colony size influences queen egg-size regulation,
the perceived but not the physical colony size of small colonies was
extended. The queens in 'small' colonies, producing relatively large eggs,
were paired via a double-screened tunnel with medium-sized hive boxes that
either contained empty frames or a queenless, 'medium' colony. All three
queens paired with a regular colony reduced the size of their eggs compared
to their initial egg size (Q1: F(3,76) = 34.5, p<0.001; Q2: F(3,76) = 42.5,
p<0.001; Q3: F(3,76) = 14.6, p<0.001; post-hoc tests indicated significant
differences only between measurements before and after manipulation.
To compare the ovary proteome of queens producing large eggs with that of
queens producing small eggs, we identified a total of 2022 proteins and
compared their relative abundance. Among the 290 proteins that exhibited
significant quantitative differences, significantly more proteins were more
abundant (275) than less abundant (15) in large-egg-producing ovaries
compared to small-egg-producing ovaries (÷2 = 233.1, p<0.001.
Across individuals from all treatment groups, Rho1 expression at the end of
the experiment correlated almost perfectly with the produced egg size.
Here, we provide evidence that egg size - a quantitative measure of maternal
provisioning - is actively adjusted by honey bee queens in response to
social cues that relate to colony size. We also find that queens in smaller
colonies have smaller ovaries, presumably because they produce fewer but
larger eggs. We find that protein localization, cytoskeleton organization,
and energy generation are key proteomic changes in the ovary that mediate
the production of large eggs. Finally, we identify the cytoskeleton
organizer Rho1 as a potentially important regulator of the active egg-size
adjustment of honey bee queens.
. little evidence for a trade-off between egg size and number was found in a
previous study of honey bee queens (
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib6> Amiri et al.,
2020). In contrast, a negative relation between egg size and number was
found here, at least in the majority of comparisons between queens in small
and large colonies. Queens in large colonies typically produce more eggs
than queens in small colonies. Our finding that queens in large colonies
have heavier ovaries indicates a physiological adaptation to satisfy the
egg-laying demand in large colonies (
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib3> Al-Khafaji et
al., 2009). However, this result cannot explain why queens in smaller
colonies produce larger eggs, why a temporary cessation of egg laying by
queens in large colonies does not lead to an increase in egg size, and why
queens decrease egg size upon their perception of being in a larger colony.
The vast majority (almost 95%) of differently abundant proteins are found at
higher levels in ovaries that produce large eggs. Thus, the anatomically
smaller ovaries are physiologically more active in several key processes
than the larger ovaries that produce smaller eggs. The GO enrichment
analysis indicates the prominence of two upregulated processes in
large-egg-producing ovaries - 'protein localization' and 'cytoskeletal
regulation' - while several energy metabolic processes are highlighted by
the KEGG pathway analysis. These functional categories indicate that
egg-size variation is not a simple increase of egg volume but reflects real
differences in offspring provisioning, although the proteome of small and
large eggs remains to be characterized (
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib40>
McDonough-Goldstein et al., 2021). Higher energy generation may be needed to
produce more costly large eggs (
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib67> Wheeler,
1996), and the cytoskeleton and protein localization processes are key to
loading the eggs with nutrients in polytrophic ovaries (
<https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib53> Shimada et
al., 2011; <https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9747152/#bib68>
Wilson et al., 2011). Several of the other GO terms, such as 'multicellular
organism development' and 'oocyte construction,' are further plausible
candidates to explain some of the observed variation in egg size.
***********************************************
The BEE-L mailing list is powered by L-Soft's renowned
LISTSERV(R) list management software. For more information, go to:
http://www.lsoft.com/LISTSERV-powered.html
|