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First published online August 22, 2008
Journal of Experimental Biology 211, 2773-2778 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.019133
Methyl farnesoate couples environmental changes to testicular development in the crab Carcinus maenas
Department of Biology, University of Central Florida, Orlando, FL 32816, USA
* Author for correspondence (e-mail: dborst{at}mail.ucf.edu)
Accepted 16 June 2008
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Summary |
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 TOP Summary INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Key words: methyl farnesoate, testis, crustacean, salinity, reproduction, temperature
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INTRODUCTION |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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;
Hoang et al., 2002;
Carmona-Osalde et al., 2004).
However, the hormonal mechanisms that mediate these environmental effects are
largely unknown. It is well established that crustacean reproduction can be
affected by eyestalk neuropeptides [e.g. gonad-stimulating and
gonad-inhibiting hormones (Huberman,
2000; Borst, 2003;
Ye et al., 2006)]. More
recently, it has been shown that reproduction can be stimulated by methyl
farnesoate (MF), a crustacean sesquiterpene related to the insect juvenile
hormone. MF production is also regulated, in part, by eyestalk neuropeptides
(Borst et al., 2001;
Nagaraju, 2007). Finally, it
has been shown that hemolymph levels of MF respond to environmental factors
such as salinity and temperature (Lovett
et al., 1997; Lovett et al.,
2001). Thus, it seems plausible that MF is an endocrine link
between the environment, eyestalk peptides and reproduction in
crustaceans.
A useful model system for such studies is the green crab (also known as the
shore crab) Carcinus maenas, an abundant crustacean found in rocky
intertidal zones (Menge,
1995). This species was introduced to the East Coast of North
America from Europe in the early nineteenth century and reached the West Coast
approximately 20years ago (Cohen et al.,
1995). These euryhaline crabs can tolerate a wide range of
salinities (1.4–52 ppt salinity) and temperatures (0–30°C)
(Crothers, 1968;
Cohen et al., 1995). Most
importantly, many of the eyestalk neuropeptides in this species have been
identified (Webster, 1998),
and hemolymph levels of MF can be manipulated by salinity
(Lovett et al., 2001).
C. maenas can have a range of colors on its ventral surface (e.g.
light green, yellow, orange and red). Nevertheless, these crabs are usually
divided into two groups: green-phase crabs and red-phase crabs
(Kaiser et al., 1990;
McKnight et al., 2000). As one
of these colors is the green phase, we will refer to individuals of C.
maenas hereafter simply as `crabs' to avoid the cumbersome term
`green-phase green crabs'.
These color phases differ substantially in terms of their physiology and
behavior. Green-phase animals tend to be smaller than red-phase animals and
molt more frequently. However, after they become red-phase animals, they molt
infrequently (Kaiser et al.,
1990; McGaw et al.,
1992; Reid et al.,
1997; Wolf, 1998).
Red-phase crabs are generally more sensitive to environmental stress than
green-phase crabs; they extract oxygen from seawater less effectively and are
less tolerant of hypoxia (Reid and
Aldrich, 1989). Red-phase crabs are less effective osmoregulators
and have higher mortality rates when exposed to low salinity seawater
(Reid et al., 1989;
McGaw and Naylor, 1992a;
McGaw and Naylor, 1992b).
However, red-phase animals are more robust (thicker carapace, larger chela
muscles) and aggressive and have greater mating success than green-phase
animals. These, and other observations, have led to suggestions that the two
color phases represent a trade-off between molting and mating. Green-phase
crabs put most of their resources into rapid growth but when they become
red-phase crabs they put most of their resources into reproduction
(Reid et al., 1997).
These physiological and behavioral differences affect the environments the
crabs inhabit. Red-phase animals tend to live in deeper water along open
shores where the water is cooler and is closer to full-strength seawater. By
contrast, green-phase crabs migrate into inlets and estuaries during high tide
during the summer (Crothers,
1968; Hunter and Naylor,
1993; Warman et al.,
1993). Thus, green-phase animals are more likely to experience
higher water temperatures and brackish water during the summer compared with
red-phase crabs.
In the present study, we show that red-phase crabs are more likely to have detectable MF in their hemolymph than green-phase crabs. In addition, the testicular index (TI) of red-phase animals is higher than that in green-phase animals. Furthermore, our results indicate that environmental factors differentially affect MF levels in the two color phases. These results are consistent with the hypothesis that MF stimulates testicular development. To test this hypothesis, we show that environmental factors that increase MF levels also stimulate testicular development. The MF levels in these two color phases appear to be responsible, in part, for the different reproductive activities of these males.
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MATERIALS AND METHODS |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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). None of
the experimental animals was missing appendages. At the end of some
experiments, the testes were removed and weighed, and the TI (% total body
mass) was calculated. Crabs were kept in large tanks containing artificial SW
(Instant Ocean, Spectrum Brands; Atlanta, GA, USA) at normal salinity (33 ppt)
at 11 or 18°C. Crabs were fed on squid and shrimp twice weekly. Animals
were acclimated to the tanks for at least a week before being used in
experiments.
Treatments
For some experiments, crabs were given a hyposalinity challenge by placing
them in dilute SW (5 ppt) at 11 or 18°C for 24 h. MF levels were analyzed
by taking hemolymph samples (0.5 ml) immediately prior to the transfer and 24
h later at the end of the challenge. Studies with [14C]inulin
indicate that the hemolymph volume of these animals ranges from 20 to 25% of
their wet body mass (G.P.C.N. and D.W.B., unpublished data), hence 0.5 ml of
hemolymph is approximately 4% of the crab's total hemolymph volume. Previous
studies demonstrate that MF levels are not affected by this sampling frequency
or volume (Lovett et al.,
2001). Some animals were bilaterally eyestalk-ablated (ESA) by
removing the eyestalks and then applying boric acid powder and Vaseline®
to the wound. Animals were anesthetized on ice for at least 10 min prior to
surgery or dissection. These animals were bled one day prior to ESA and then
at the indicated times after ESA. Some animals were bled sequentially but
never more frequently than 24 h.
Measurement of methyl farnesoate (MF) levels
Hemolymph levels of MF were determined using a high-performance liquid
chromatography (HPLC) method that has been previously described and validated
for C. maenas (Borst and
Tsukimura, 1991). Briefly, hemolymph (0.5 ml unless otherwise
noted) was withdrawn through the arthrodial membrane of the coxa of a walking
leg. It was added to 2.5 ml acetonitrile and 4% NaCl to give a total volume of
4.5 ml. The mixture was extracted with 1.5 ml hexane containing 20 ng of
cis,trans-MF (used as an internal standard) and the hexane
supernatant was analyzed by normal-phase HPLC (silica column; 1.9% diethyl
ether in hexane; 220 nm). We calculated the MF content of each sample by
comparing its MF peak area with that of an MF standard. The lower limit of MF
detection was 2 ng ml–1.
Effect of salinity, temperature, ESA and MF treatment on testicular development
Male green-phase crabs were acclimated to 33 ppt SW at 11°C for at
least one week. As stress often causes a small transient rise in MF levels
(Lovett et al., 2001), the
handling of these animals was limited and they were not bled. Some males were
treated with 1 µg MF (Echelon Biosciences; Salt Lake, UT, USA). As MF is
hydrophobic, we limited adsorption loss by suspending it, immediately prior to
injection, in modified Pantin's saline
(Laufer et al., 1987)
containing 5% ethanol and 1% bovine serum albumin (BSA; Sigma-Aldrich Chemical
Co., St Louis, MO, USA). Control animals were treated with the vehicle
solution. MF and vehicle-treated animals were injected with 200 µl of the
solution, through the arthrodial membrane of the coxa of the third walking
leg, on days one, five and 10. The TI values of these animals were determined
on day 15.
In a second experiment, males were treated with temperature, hyposalinity or ESA. Group 1 crabs (the initial control) were dissected on the first day of the experiment. Crabs in group 2 (intact) and group 3 (ESA) were maintained in 33 ppt SW at 11°C. Crabs in groups 4 and 5 were held in 18°C SW with a salinity of 33 ppt or 5 ppt, respectively. Animals from groups 2–5 were dissected on day 15, and their TI values were determined. No deaths or injuries occurred during the experiment.
Statistical analysis
The data were analyzed using Instat Software (GraphPad; San Diego, CA,
USA). A two-tailed t-test was used to compare MF levels between the
two different treatment groups. For data expressed as the percentage of a
population, Fisher's exact test was used. Data with multiple groups were
analyzed by one-way analysis of variance (ANOVA) followed by the
Student–Newman–Keuls test to determine significance.
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RESULTS |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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). In red-phase males, a hyposalinity challenge increased the
percentage of animals with detectable MF from 37% to 94% at 11°C
(P<0.001) and from 30% to 92% at 18°C (P<0.001)
(Fig. 2A). Whereas low salinity
increased the percentage of animals that had detectable levels of MF at either
temperature, the amount of MF in the hemolymph of those animals with
detectable MF did not significantly change
(Fig. 2B).
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Since acclimation to SW at 18°C might induce the enzymes of the MF synthetic pathway, we also investigated the effect of ESA on red- and green-phase males in 33 ppt SW at 11°C. Red-phase males were analyzed for MF approximately one week prior to ESA, and only those animals that had no detectable MF were included in this study. None of the animals in either color phase had detectable MF in hemolymph samples taken one day prior to ESA, whereas every animal in both groups had detectable MF 24 h after ESA. The MF levels of green-phase males (6.2±0.9 ng ml–1, N=6) 24 h after ESA were significantly (P<0.001; t-test) lower than the levels observed in red-phase males (21.8±5.3 ng ml–1, N=5). However, MF levels in green-phase males rose over time and on day 5 reached a level that was similar to the levels observed in red-phase males (Fig. 3A).
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The above data indicate that environmental factors (e.g. temperature and salinity) can affect MF production in C. maenas. We tested the potential impact of such factors on male reproduction. Green-phase males were initially housed in 33 ppt SW at 11°C. In one study, MF levels were increased by injecting males with 1 µg MF on days one, five and 10 while control animals were treated with the vehicle (Fig. 4A). By day 15, the TI of the MF-treated animals had increased by 119% (P<0.01; t-test). The TI of these treated animals was similar to the TI observed earlier in red-phase males (Fig. 1B).
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DISCUSSION |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Red-phase males were much more likely to have MF in their hemolymph
compared with green-phase animals. This observation correlates with the high
TIs of red-phase animals, consistent with the idea that MF stimulates
testicular growth either directly or indirectly in crustaceans
(Kalavathy et al., 1999;
Nagaraju et al., 2003;
Nagaraju et al., 2006;
Reddy et al., 2004). These
observations are similar to previous studies in the spider crab (Libinia
emarginata), which demonstrated a correlation between the reproductive
status of males and MF synthesis by the mandibular organ (MO) and hemolymph
levels of MF (Sagi et al.,
1993; Sagi et al.,
1994). It should be noted that the correlations between MF levels
and male reproduction are weak, since the majority of the red-phase males do
not show detectable MF but still have a high TI. The most likely explanation
for this is that the spontaneous release of MF is episodic
(Borst and Tsukimura, 1992) and
the half-life of MF is short. In the lobster Homarus americanus, we
estimated that the half-life of MF is less than 60 min
(Tsukimura and Borst, 1992).
However, a sustained elevation of MF does not appear to be necessary for a
biological effect. MF treatments, such as those shown in
Fig. 4A, would only cause a
transient elevation of MF in these animals. Nevertheless, this treatment still
affected testicular growth significantly.
Our data show that the two color phases differ profoundly in their
responses to temperature and salinity. Previous studies showed that MF levels
in C. maenas males increase when animals are exposed to dilute SW for
more than 8 h (Lovett et al.,
2001). In the Lovett et al. study, only green-phase animals were
used because red-phase animals gave inconsistent results. These observations
were confirmed by the current study. Untreated red-phase animals often have
detectable MF, and the levels in these animals were similar to the levels
observed in animals that responded to low salinity. Another significant
difference between the two color phases is the temperature dependence of their
response to a hyposalinity challenge. Red-phase males responded to a challenge
at both temperatures (11 and 18°C) whereas green-phase males were only
responsive at 18°C.
Eyestalk removal has been shown to increase MF levels in a wide variety of
crustaceans, including L. emarginata
(Laufer et al., 1987),
Cancer pagurus (Borst et al.,
2002), Callinectes sapidus
(Henry and Borst, 2006) and
Oziotelphusa senex senex
(Nagaraju et al., 2005).
Consistent with these observations, ESA increased MF levels in both green- and
red-phase C. maenas males at 11°C. Clearly, green-phase animals
can synthesize MF when held at 11°C. Thus, their lack of a response to
hyposalinity at 11°C does not reflect an inability to produce MF.
Nevertheless, the levels of MF observed in green-phase males 24 h after ESA
were significantly lower than those observed in red-phase males. This suggests
that the initial synthesis capacity of green-phase males is not as great as it
is in red-phase males. The difference in MF levels between green- and
red-phase animals disappears 5 days after ESA. This probably reflects the
hypertrophy of the MO, which is known to occur after ESA
(Borst et al., 1994;
Nagaraju et al., 2004).
Although a hyposalinity challenge had no significant effect on the MF levels of green- or red-phase animals after ESA, there was a modest effect in SW at 18°C. This suggests that the eyestalk is the major regulator of MF levels in response to salinity. By contrast, temperature significantly affected the MF levels of ESA animals. It is unclear whether this is due to a temperature effect on overall metabolism or to a regulatory mechanism that is eyestalk independent.
Several compounds may regulate MF production by the MO, some of which are
found in the eyestalk. Indeed, the simplest explanation for the elevation of
MF levels of C. maenas, and other crustaceans, after ESA is that the
eyestalk contains a compound that directly inhibits MF production by the MO.
Several putative MO-inhibiting hormones (MOIHs) have been isolated from the
sinus glands of C. pagurus
(Wainwright et al., 1996) and
L. emarginata (Liu and Laufer,
1996). Although these peptides can decrease MF synthesis by MO
in vitro, they have not been shown to function as MOIHs in
vivo. Indeed, relatively large amounts of both peptides are required to
inhibit the MO in vitro, arguing against their role in regulating
this gland in vivo. The sinus glands of C. pagurus and
H. americanus contain another, as yet unidentified, peptide that
inhibits MF production in vivo but does not appear to act directly on
the MO (Borst et al., 2002). In
addition, allatostatin has been shown to stimulate MF production by MO in
vitro (Kwok et al.,
2005), although it has not been shown to affect MF production
in vivo. Clearly, more work needs to be done before we fully
understand the mechanisms involved in regulating MF synthesis by this
tissue.
Our present study provides strong evidence that MF has an important role in
regulating male testicular development. A role for MF in male reproduction has
been inferred from several previous studies. For example, the size of the MO
in the male lobster (H. americanus) increases after sexual maturity
(Waddy et al., 1995).
Likewise, MF synthesis rates by spider crab MO incubated in vitro
were correlated with reproductive behavior
(Sagi et al., 1993;
Sagi et al., 1994). In
addition, MF treatment has been shown to increase testicular growth in a
number of crustacean species, including the freshwater field crab O. senex
senex (Kalavathy et al.,
1999; Reddy et al.,
2004), and the freshwater prawn Macrobrachium
malcholamsonii (Nagaraju et al.,
2003). Our observations confirm these previous studies and
demonstrate that MF treatment can stimulate testicular growth in green-phase
animals.
The eyestalk is also known to regulate testicular function in crustaceans.
tsu found that the removal of eyestalks from young male Potama
dehaani resulted in a rapid increase in the size of the testes and male
genital ducts (tsu,
1961). Likewise, ESA of Litopenaeus vannamei increased
their testicular index and doubled mating frequency
(Chamberlain and Lawrence,
1981). These, and other, studies have led to the proposal that the
eyestalk contains a gonad-inhibiting hormone (GIH)
(Kulkarni et al., 1984;
Ye et al., 2006). In the
present investigation, we demonstrate that ESA stimulates testicular growth in
green-phase males of C. maenas. As ESA increases MF levels, and MF
treatment alone can stimulate testicular growth, it seems likely that MF
couples ESA to gonad growth in these animals. However, it should be noted that
the green-phase males used in this study were large and were presumably
nearing sexual maturity. If so, their responses to environmental conditions
and other treatments may be different from the responses that would occur in
younger (smaller) green-phase males. At younger stages, ESA may affect
testicular development via mechanisms that do not include MF.
Finally, our present data show that environmental factors, such as
temperature and salinity, can affect MF levels and thereby stimulate
testicular growth. During the summer, green-phase animals are abundant in
estuaries (Crothers, 1968;
Hunter and Naylor, 1993;
Warman et al., 1993), where
the water is likely to be brackish and warmer. Thus, it seems likely that
green-phase crabs will have a larger TI at the end of this season. Whether
green-phase crabs seek an estuarine environment because it stimulates MF
production and thereby increases gonad growth is not clear. Nevertheless,
these observations provide a unique insight into how behavior, the environment
and physiology might interact in the reproductive strategies of this
crustacean. Determining these interactions will afford a more comprehensive
view of how reproduction is regulated in this species and probably other
crustaceans.
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Acknowledgments |
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References |
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TOPSummaryINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
|---|
Borst, D. W. (2003). Crustacean endocrine systems. In Encyclopedia of Hormones (ed. H. L. Henry and A. W. Norman), pp. 340-351. Amsterdam: Elsevier.
Borst, D. W. and Tsukimura, B. (1991). Quantification of methyl farnesoate levels in hemolymph by high-performance liquid chromatography. J. Chromatogr. 545, 71-78.[CrossRef][Medline]
Borst, D. W. and Tsukimura, B. (1992). Methyl farnesoate levels in crustaceans. In Insect Juvenile Hormone Research: Fundamental and Applied Approaches (ed. B. Mauchamp, F. Couillaud and J. C. Baehr), pp. 27-35. Paris: Institut National de la Recherche Agronomique.
Borst, D. W., Tsukimura, B., Laufer, H. and Couch, E. F. (1994). Regional differences in methyl farnesoate production by the mandibular organ of the lobster, Homarus americanus. Biol. Bull. 186,9 -16.[Abstract]
Borst, D. W., Ogan, J., Tsukimura, B., Claerhout, T. and Holford, K. C. (2001). Regulation of the crustacean mandibular organ. Am. Zool. 41,430 -441.[CrossRef]
Borst, D. W., Wainwright, G. and Rees, H. H. (2002). In vivo regulation of the mandibular organ in the edible crab, Cancer pagurus. Proc. R. Soc. Lond. B Biol. Sci. 269,483 -490.[CrossRef][Medline]
Carmona-Osalde, C., Rodríguez-Serna, M., Olvera-Novoa, M. A. and Gutieírrez-Yurrita, P. J. (2004). Effect of density and sex ratio on gonad development and spawning in the crayfish Procambarus ilamasi. Aquaculture 236,331 -339.[CrossRef]
Chamberlain, G. W. and Lawrence, A. L. (1981). Effect of light intensity and male and female eyestalk ablation on reproduction of Penaeus stylirostris and P. vannamei. J. World Aquac. Soc. 12,357 -372.
Cohen, A. D., Carlton, J. T. and Fountain, M. C. (1995). Introduction, dispersal and potential impacts of the green crab Carcinus maenas in San Francisco Bay, California. Mar. Biol. 122,225 -237.
Crothers, J. H. (1968). The biology of the shore crab, Carcinus maenas (L.). 2. The life of the adult crab. Field Studies 2,579 -614.
Henry, R. P. and Borst, D. W. (2006). Effects of eyestalk ablation on carbonic anhydrase activity in the euryhaline blue crab Callinectes sapidus: neuroendocrine control of enzyme expression. J. Exp. Zool. 305, 23-31.
Hoang, T., Lee, S. Y., Keenan, C. P. and Marsden, G. E. (2002). Effect of temperature on spawning of Penaeus merguiensis. J. Therm. Biol. 27,433 -437.[CrossRef]
Huberman, A. (2000). Shrimp endocrinology. A review. Aquaculture 191,191 -208.[CrossRef]
Hunter, E. and Naylor, E. (1993). Intertidal migration by the shore crab Carcinus maenas. Mar. Ecol. Prog. Ser. 101,131 -138.[CrossRef]
Kaiser, M. J., Hughes, R. N. and Reid, D. G. (1990). Chelae morphometry, prey-size selection and aggressive competition in green and red forms of Carcinus maenas (L.). J. Exp. Mar. Biol. Ecol. 140,121 -134.[CrossRef]
Kalavathy, Y., Mamatha, P. and Reddy, P. S. (1999). Methyl farnesoate stimulates testicular growth in the freshwater crab Oziotelphusa senex senex Fabricius. Naturewissenschaften 86,394 -395.[CrossRef]
Kulkarni, G. K., Nagabhushanam, R. and Joshi, P. K. (1984). Neuroendocrine control of reproduction in the male penaeid prawn, Parapenaeopsis hardwickii (Miers) (Crustacea, Decapoda, Penaeidae). Hydrobiologia 108,281 -289.
Kwok, R., Zhang, J. R. and Tobe, S. S. (2005). Regulation of methyl farnesoate production by mandibular organs in the crayfish, Procambarus clarkii; a possible role for allatostatins. J. Insect Physiol. 51,367 -378.[CrossRef][Medline]
Laufer, H., Borst, D. W., Baker, F. C., Carrasco, C., Sinkus,
M., Reuter, C. C., Tsai, L. W. and Schooley, D. A. (1987).
Identification of a juvenile hormone-like compound in a crustacean.
Science 235,202
-205.
Liu, L. and Laufer, H. (1996). Isolation and characterization of sinus gland neuropeptides with both mandibular inhibiting hormone and hyperglycemic effects from the spider crab, Libinia emarginata. Arch. Insect. Biochem. Physiol. 32,375 -385.[CrossRef]
Lovett, D. L., Clifford, P. D. and Borst, D. W. (1997). Physiological stress elevates hemolymph levels of methyl farnesoate in the green crab Carcinus maenas. Biol. Bull. 193,266 -267.
Lovett, D. L., Verzi, M. P., Clifford, P. D. and Borst, D. W. (2001). Hemolymph levels of methyl farnesoate increase in response to osmotic stress in the green crab Carcinus maenas. Comp. Biochem. Physiol. 128,299 -306.
McGaw, I. J. and Naylor, E. (1992a). Salinity preference of the shore crab Carcinus maenas in relation to coloration during inter-moult and to prior acclimation. J. Exp. Mar. Biol. Ecol. 155,145 -159.[CrossRef]
McGaw, I. J. and Naylor, E. (1992b). Distribution and rhythmic locomotor patterns of estuarine and open-shore populations of Carcinus maenas. J. Mar. Biolog. Assoc. UK 72,599 -609.
McGaw, I. J., Kaiser, M. J., Naylor, E. and Hughes, R. N. (1992). Intraspecific morphological variation related to the moult-cycle in colour forms of the shore crab Carcinus maenas. J. Zool. (Lond.) 228,351 -359.
McKnight, A., Mathews, L. M., Avery, R. and Lee, K. T. (2000). Distribution is correlated with color phase in green crabs, Carcinus maenas (Linnaeus, 1758) in southern New England. Crustaceana 73,643 -770.[CrossRef]
Menge, B. A. (1995). Indirect effects in marine rocky intertidal interaction webs: Patterns and importance. Ecol. Monogr. 65,21 -74.[CrossRef]
Nagaraju, G. P. C. (2007). Is methyl farnesoate a crustacean hormone? Aquaculture 272, 39-54.[CrossRef]
Nagaraju, G. P. C., Suraj, N. J. and Reddy, P. S. (2003). Methyl farnesoate stimulates gonad development in Macrobrachium malcolmsonii Milne Edwards. Crustaceana 76,1171 -1178.[CrossRef]
Nagaraju, G. P. C., Reddy, P. R. and Reddy, P. S. (2004). Mandibular organ, its relation to body weight sex molt and reproduction in the crab Oziotelphusa senex senex Fabricius (1791). Aquaculture 232,603 -612.[CrossRef]
Nagaraju, G. P. C., Prasad, G. L. V. and Reddy, P. S. (2005). Isolation and characterization of mandibular organ-inhibiting hormone from the eyestalks of freshwater crab, Oziotelphusa senex senex. Int. J. Appl. Sci. Eng. 3, 61-68.
Nagaraju, G. P. C., Reddy, P. R. and Reddy, P. S. (2006). In vitro methyl farnesoate secretion by mandibular organs isolated from different molt and reproductive stages of the crab Oziotelphusa senex senex. Fish. Sci. 72,410 -414.[CrossRef]
tsu, T. (1961). The accelerating
influence of eyestalk ablation on spermatogenesis and on development of the
male genital ducts in young Potamon dehaani. Bull. Yamagata Univ.
Ser. Nat. Sci. 5,379
-383.
Reddy, P. R., Nagaraju, G. P. C. and Reddy, P. S. (2004). Involvement of methyl farnesoate in the regulation of molting and reproduction in the freshwater crab Oziotelphusa senex senex.J. Crust. Biol. 24,511 -515.[CrossRef]
Reid, D. G. and Aldrich, J. C. (1989). Variation in responses to environmental hypoxia of different colour forms of the shore crab Carcinus maenas (L.). Comp. Biochem. Physiol. 92,535 -539.
Reid, D. G., Abelló, P., McGaw, I. and Naylor, E. (1989). Differential tolerances of desiccation and hypo osmotic stress in sub- and inter-tidal Carcinus maenas. In Phenotypic Responses in Aquatic Ectotherms (ed. J. C. Aldrich), pp. 89-96. Japaga: Dublin.
Reid, D. G., Abelló, P., Kaiser, M. J. and Warman, C. G. (1997). Carapace colour, inter-moult duration and the behavioural and physiological ecology of the shore crab Carcinus maenas.Estuar. Coast. Shelf Sci. 44,203 -211.[CrossRef]
Robertson, L., Bray, W. and Lawrence, A. (1991). Reproductive response of Penaeus stylirostris to temperature manipulation. J. World Aquac. Soc. 22,109 -117.[CrossRef]
Sagi, A., Homola, E. and Laufer, H. (1993). Distinct reproductive types of male spider crabs Libinia emarginata differ in circulating and synthesizing methyl farnesoate. Biol. Bull. 185,168 -173.[Abstract]
Sagi, A., Ahl, J. S. B., Danaee, H. and Laufer, H. (1994). Methyl farnesoate levels in male spider crabs exhibiting active reproductive behavior. Horm. Behav. 28,261 -272.[CrossRef][Medline]
Tsukimura, B. and Borst, D. W. (1992). Regulation of methyl farnesoate in the hemolymph and mandibular organ of the lobster, Homarus americanus. Gen. Comp. Endocrinol. 86,297 -303.[CrossRef][Medline]
Waddy, S. L., Aiken, D. E. and de Kleijn, D. P. V. (1995). Control of growth and reproduction. In Biology of the Lobster Homarus americanus (ed. J. R. Factor), pp.217 -266. San Diego: Academic Press.
Wainwright, G., Webster, S. G., Wilkinson, M. C., Chung, J. S.
and Rees, H. H. (1996). Structure and significance of
mandibular organ-inhibiting hormone in the crab Cancer pagurus. J.
Biol. Chem. 271,12749
-12754.
Warman, C. G., Reid, D. G. and Naylor, E. (1993). Variation in the tidal migratory behaviour and rhythmic light-responsiveness in the shore crab, Carcinus maenas. J. Mar. Biol. Assoc. UK 73,355 -364.
Webster, S. G. (1998). Neuropeptides inhibiting growth and reproduction in crustaceans. In Recent Advances in Arthropod Endocrinology (ed. G. M. Coast and S. G. Webster), pp.33 -52. Cambridge: Cambridge University Press.
Wolf, F. (1998). Red and green colour forms in the common shore crab Carcinus maenas (L.) (Crustacea: Brachyura: Portunidae): Theoretical predictions and empirical data. J. Nat. Hist. 32,1807 -1812.[CrossRef]
Ye, H., Huang, H., Li, S., Wang, G. and Li, Q. (2006). In vitro study of neuroendocrine regulation over the testicular development in mud crabs Scylla serrata. Chinese J. Oceanol. Limnol. 24,142 -146.[CrossRef]
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