Integrative and Comparative Biology
Integrative and Comparative Biology, volume 52, number 6, pp. 792–800
doi:10.1093/icb/ics091
Society for Integrative and Comparative Biology
SYMPOSIUM
Environmental Physiology of the Mangrove Rivulus,
Kryptolebias marmoratus, A Cutaneously Breathing Fish
That Survives for Weeks Out of Water
Patricia A. Wright1
Department of Integrative Biology, University of Guelph, Guelph, ON, Canada N1G 2W1
From the symposium ‘‘Mangrove ‘Killifish’: An Exemplar of Integrative Biology’’ presented at the annual meeting of the
Society for Integrative and Comparative Biology, January 3–7, 2012 at Charleston, South Carolina.
1
E-mail: [email protected]
Synopsis The mangrove rivulus (Kryptolebias marmoratus) is an excellent model species for understanding the physiological mechanisms that fish use in coping with extreme environmental conditions, particularly cutaneous exchange
during prolonged exposure to air. Their ability to self-fertilize and produce highly homozygous lineages provides the
potential for examining environmental influences on structures and related functions without the complications of
genetic variation. Over the past 10 years or so, we have gained a broader understanding of the mechanisms
K. marmoratus use to maintain homeostasis when out of water for days to weeks. Gaseous exchange occurs across the
skin, as dramatic remodeling of the gill reduces its effective surface area for exchange. Ionoregulation and osmoregulation
are maintained in air by exchanging Naþ, Cl, and H2O across skin that contains a rich population of ionocytes.
Ammonia excretion occurs in part by cutaneous NH3 volatilization facilitated by ammonia transporters on the surface
of the epidermis. Finally, new evidence indicates that cutaneous angiogenesis occurs when K. marmoratus are emersed for
a week, suggesting a higher rate of blood flow to surface vessels. Taken together, these and other findings demonstrate
that the skin of K. marmoratus takes on all the major functions attributed to fish gills, allowing them to move between
aquatic and terrestrial environments with ease. Future studies should focus on variation in response to environmental
changes between homozygous lineages to identify the genetic underpinnings of physiological responses.
Introduction
The environment, whether aquatic or terrestrial, has
had a large impact on the evolution of structure and
function in animals. If one considers respiratory
structures, for example, breathing water is challenging
because it is 800 times more dense, 60 times more
viscous, and contains 30 times less oxygen relative to
air (Dejours 1988). Consequently, gills in extant fishes
are highly efficient at extracting oxygen. Air breathers
can breathe fewer breaths relative to water breathers
to take up the same amount of oxygen (Dejours
1974). However, the greatest challenge for air breathers is dehydration. Over evolutionary time, the benefits of breathing air must have outweighed the costs
because more than 370 species of air-breathing fish
are known (Graham 1997). So what’s so special about
Kryptolebias marmoratus—is it just one of many or is
it a remarkable species that can provide us with novel
insights into the physiology of breathing air? I will
argue the latter for three key reasons: (1) these fish
are self-fertilizing, (2) tolerant of extreme environments, and (3) they completely rely on cutaneous
respiration when out of water.
Self-fertilization
K. marmoratus are self-fertilizing hermaphrodites
(Harrington 1961; Tatarenkov et al. 2009) and produce highly homozygous lineages when isolated in
the laboratory for many generations (Vrijenhoek
1985; Turner et al. 1990). Wild populations
are androdioecious; males occur at low, but variable, rates and outcrossing between males and
Advanced Access publication June 12, 2012
The Author 2012. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.
For permissions please email: [email protected].
Environmental physiology of the mangrove rivulus
hermaphrodites is thought to be the cause of heterozygosity (see Tatarenkov this issue). For physiologists
interested in the effects of environment on the phenotype (e.g. structure, function), the ability to study
isogenic laboratory strains eliminates the confounding factor of genotype. Further, if differences in
physiological responses to environmental change are
detected between isogenic strains and between wild
populations, then a more detailed differential genetic
screening may provide new insights into regulatory
pathways. For example, acclimation to changing environmental salinity is variable among lineages of
K. marmoratus. We have discovered that in hypersaline water, some lineages remodel their gills and decrease the effective surface area for exchange,
presumably limiting excessive ion uptake (discussed
below), whereas other lineages show no response (A.
Turko and P. Wright, unpublished data). If the gene
and/or protein expression profiles of the gills from
lineages showing a differential response to salinity are
compared, then the genes and proteins responsible
for regulating remodeling of the gills could be identified. In addition, comparing plasma hormone profiles among those fish that do undergo changes in
the gills and those that do not would be one step
toward understanding whether gill remodeling in response to salinity is under endocrine control. A comparative genomics approach has been used in
euryhaline Fundulus sp. to identify the importance
of particular genes in acclimation to salinity and in
physiological systems that may be linked to osmotic
tolerance and niche segregation (Whitehead 2012).
To date, physiologists have not capitalized on this
opportunity in K. marmoratus. Significant progress
has been made in understanding the genetics of
K. marmoratus (see Tararenkov this issue) and the
annotated genome of multiple lineages is soon to be
available (see Kelly this issue). In addition, identifying phenotypic differences in growth and behavior
between isogenic lineages (see Earley this issue)
is valuable information when assessing which lineages are most suited for specific environmental manipulations. Thus, in the next few years, there is
potential for great gains and novel insights to be
made in determining the factors controlling physiological responses to environmental change using
K. marmoratus as a model species.
Extremophilic
The second reason why K. marmoratus are of particular physiological interest is that they thrive under
relatively extreme conditions. Physiologists interested
in understanding the underlying mechanisms of a
793
response to the environment may gain more information from an animal that is surviving at the limits
of tolerance rather than an organism that tolerates
only moderate conditions. Textbooks of comparative
animal physiology routinely present this tenet in
their opening pages as the August Krogh Principle
‘‘For every well-defined physiological problem there
is an animal optimally suited to yield an answer’’
(Randall et al. 2002). For example, if one is
interested in the physiological consequences of
air-breathing in fish, more insight may be gained
from studying K. marmoratus that survives for 2
months out of water (emersed) compared with a
species that gulps air occasionally at the surface of
the water.
The extreme nature of the habitat of
K. marmoratus is readily apparent by taking a walk
through the mangrove forests of the western Atlantic
region (Taylor et al. 1995; see also Taylor this issue).
Progress is slow as you climb over a tangle of aerial
roots from the red mangrove trees and sink deep
into the thick mud where microbial activity releases
malodorous hydrogen sulphide from deep layers of
decaying vegetation. K. marmoratus typically reside
in crab burrows (8.0 0.5 cm [diameter] 33.9 2.0 cm [long], n ¼ 13) (P. Wright and D.S.
Taylor, unpublished data) on the forest floor.
Water quality for aquatic respiration in these crab
burrows could not be worse—the water is extremely
hypoxic (Fig. 1), has elevated levels of H2S (Abel
et al. 1987), and is warm (25–308C) (Davis et al.
1990; Taylor 2000; Frick and Wright 2002a). We
measured dissolved oxygen (DO) levels in crab burrows where K. marmoratus were found on Calabash
Caye in December 2009 over a 24-h period (Fig. 1;
see also Ellison et al. 2012). Normally, fully
air-saturated water at these temperatures and salinity
would contain 7.5 mg L1 DO; however, mean DO
in the crab burrows was 51 mg L1, a level of oxygen
few aquatic species tolerate for long. Earlier studies
on K. marmoratus reported that the fish were insensitive to hypoxia alone but emersed when exposed to
a combination of elevated H2S (0.003 mg L1) and
mild hypoxia (2 mg L1 DO) (Abel et al. 1987).
Obviously K. marmoratus are tolerant of extreme
water conditions, but emersion may be a convenient
escape when environmental conditions are beyond
the range of tolerance.
Using a remote video camera, we recorded activity
at the surface of a crab burrow in Calabash Caye,
Belize (see Supplementary Video). Several mangrove
rivulus were observed resting on a small branch at
the air–water interface. At the same time, the crab
Cardisoma guanhumi rose to the surface from deep
794
P. A. Wright
Fig. 1 DO levels in three neighboring crab burrows (site 1) on Calabash Caye, Belize, at the end of the wet season (December 2009)
over a 24-h period. Note that fully oxygenated water (288C, 38ø) would have a DO level of 7.5 mg L1 (P. Wright et al.,
unpublished data). Means S.E. (n ¼ 3).
within the burrow and aerated its gills. No doubt
aerial respiration for both animals is a routine and
possibly necessary daily behavior due to the severely
hypoxic water in which they reside. To our knowledge, there have been no studies quantifying the
amount of time K. marmoratus remains immersed
in crab burrows under these conditions. This information would be valuable to assess their tolerance to
hypoxia (and H2S) in the field.
We decided to examine the emersion response in
more detail in the laboratory to carefully quantify the
threshold for breathing air in response to hypoxia.
When the oxygen content of water was acutely lowered from normoxia to hypoxia, 50% of
K. marmoratus emersed at 0.23 mg L1 DO (Fig. 2)
(Regan et al. 2011), an O2 level similar to that in
water in burrows (Fig. 1). These results demonstrate
that hypoxia alone induces emersion, in contrast to
the findings of Abel et al. (1987). The level of hypoxia used by Abel et al. (2 mg L1 DO) was well
above the threshold for emersion (50.4 mg L1
DO) found in the study by Regan et al. (2011). In
most
air-breathing
fish,
hypoxia
induces
air-breathing at higher levels of DO relative to
K. marmoratus and full emersion is typically unnecessary (Graham 1997; Chapman and McKenzie
2009). Before emersion, K. marmoratus appear to
spend more time at the surface, but a careful study
to characterize aquatic surface respiration (ASR) has
not been conducted for this species. ASR is a
common behavior in hypoxia-tolerant fish when
oxygen is depleted from deeper waters (Chapman
Fig. 2 Proportion of K. marmoratus immersed in water at low
levels of DO (DO; mg L1). At lower DO levels (50.4 mg L1),
fish emersed and adhered to the side of the experimental
chamber (N ¼ 21, EC50 ¼ 0.23 mg L1 DO). From Regan et al.
(2011).
and McKenzie 2009). What mechanisms enable
K. marmoratus to tolerate extreme hypoxia? The
answer is unknown. In fish, the short-term critical
adjustment to lower levels of oxygen in the water
that limit the mismatch between demand and
supply of oxygen is the hypoxia ventilatory response
(HVR) (Perry et al. 2009). The HVR involves an
increase in the rate of ventilation and/or the
volume of water pumped over the gills per breath.
Mangrove rivulus have a robust HVR, increasing
mostly the rate of ventilation rather than the ventilatory amplitude when water DO is lowered to 3–
5 mg L1 (A. Turko et al., submitted for publication).
795
Environmental physiology of the mangrove rivulus
It is also adaptive if fish can increase the rate of
perfusion through cardiovascular adjustments
during exposure to hypoxia, but there are no data
in this regard with respect to K. marmoratus. Longer
term resistance to hypoxia in animals has been
linked to the hypoxia inducible factor (HIF-1), a
transcription factor that controls the expression of
numerous genes controlling angiogenesis, formation
of red blood cells, glycolysis, and other pathways
(reviewed by Nikinmaa and Rees 2005). Increased
hemoglobin levels or changes in the expression of
hemoglobin isoforms toward higher-affinity isomorphs have been reported (Frey et al. 1998;
Rutjes et al. 2007; Campo et al. 2008; Wells 2009),
but, again, whether similar adjustments occur in
K. marmoratus is unknown. Investigations of HIF1 expression and downstream effects in response
to hypoxia in K. marmoratus are warranted.
Respiration in air
The third advantage of studying K. marmoratus is
that the mechanisms of cutaneous exchange in
air-breathing fishes are not completely understood.
Cutaneous respiration is not uncommon in amphibious fishes (Graham 1997; Sayer 2005), but few
depend on the skin as the sole site of exchange like
K. marmoratus does without accessory air-breathing
organs (ABOs). To maintain homeostasis in air, fish
must continue to transport O2 and CO2, balance
ions and water, and prevent the accumulation of
potentially toxic nitrogenous wastes. There is a vast
body of literature on the structure of ABOs and the
respiratory/cardiovascular changes that occur when
air-breathing fishes switch from aquatic to aerial respiration (see Hughes 1976; Graham 1997). In addition, detailed work has been carried out more
recently on various strategies for nitrogen excretion
in air-breathing fish (reviewed by Ip et al. 2001;
Sayer 2005; Chew et al. 2006). However, many questions remain. If cutaneous respiration dominates
during emersion, does the structure and function
of the skin and gills reversibly remodel to accommodate changing roles on land? Over the past decade,
researchers in my laboratory have focused on mechanisms responsible for cutaneous exchange and tissue
remodeling when K. marmoratus emerse. Highlights
from this and other work are reviewed below.
Morphological plasticity of gills
For most fish, the gills are the primary site of
exchange between the external environment and the
blood (internal environment). Gaseous exchange, excretion of nitrogenous wastes, acid–base regulation,
and osmoregulation and ionoregulation occur at the
gills (Evans et al. 2005), with the cutaneous surface
and kidneys playing a minor role in most cases. In
the absence of water, gill lamellae (also called secondary lamellae) collapse due to high surface tension, coalesce, and the fused structures reduce the
effective surface area for exchange, with irreversible
loss of function in most fish (Lam et al. 2006).
K. marmoratus may spend minutes to weeks out of
water, but gross morphology of the gill when fish are
in water (immersed) is typical of other fully aquatic
teleosts (Ong et al. 2007). There is no evidence of gill
rods, fused lamellae, or widely spaced lamellae typical of some air-breathing fish, such as the mudskipper that partially uses the gills for gaseous exchange
in air (e.g. Low et al. 1988; Lam et al. 2006). Also,
K. marmoratus do not gulp air or ventilate the opercular chamber when out of water (LeBlanc et al.
2010). Instead, K. marmoratus reversibly remodel
their gills in response to exposure to air. A cell
mass appears between the lamellae (interlamellar
cell mass [ILCM]) which effectively reduces the
gill’s surface area after a week in air; after recovery
in water, the ILCM degenerates (Fig. 3; Ong et al.
2007; Turko et al. 2011). Reversible changes in morphology of the gills were first reported in the fully
aquatic crucian carp (Carassius carassius) and closely
related goldfish (C. auratus) with changes in temperature and in oxygen content of the water, a response
that is thought to be effective in balancing oxygen
uptake with loss of ions in these freshwater species
(Sollid et al. 2003, 2005; Nilsson 2007). The physiological value of reduced surface area of the gills in
emersed K. marmoratus is unknown. Remodeling of
the gills in K. marmoratus may be a mechanism that
decreases the risk of desiccation and/or preserves lamellar structure when K. marmoratus are out of
water for extended periods (Ong et al. 2007).
Gaseous exchange
Metabolic rate does not typically decline when
amphibious fish emerse (e.g. Gordon et al. 1969;
Gordon et al. 1978; Steeger and Bridges 1995; Kok
et al. 1998; Takeda et al. 1999), although in cases
when the habitat dries aestivation is critical for survival (e.g. African lungfish; Janssen 1964). On land,
K. marmoratus requires a moist habitat and metabolic rate (as measured by excretion of CO2) is
maintained, or even enhanced, over the first 5 days
of exposure to air (Ong et al. 2007). Moreover, mitochondrial oxidative enzymes (plus seven enzymes
involved in amino acid metabolism) were unchanged
or slightly increased in K. marmoratus held for 10
796
Fig. 3 Representative light micrographs of gill filaments and
lamellae of a control K. marmoratus in water (A), a fish exposed
to air for 1 week (B), and a fish recovered in water for 1 week
after a week in air (C). Scale bar ¼ 50 mm. From Ong et al.
(2007).
P. A. Wright
days in air (Frick and Wright 2002b). These data
suggest that cutaneous respiration adequately meets
the metabolic needs of K. marmoratus at least over
the first week or so.
Gaseous exchange may be facilitated during aerial
episodes by an increase in cutaneous blood flow.
Grizzle and Thiyagarajah (1987) reported that the
dorsal epidermis of K. marmoratus contains capillaries within 1 m of the skin’s surface providing a very
short diffusion distance between air and blood. In
other amphibious species, estimated diffusion distances are slightly greater and vary considerably
(2–340 m) (e.g. Yokoya and Tamura 1992;
Graham 1997; Zhang et al. 2000; Park 2002; Park
et al. 2003). In K. marmoratus, arteriole diameter
narrows in vessels of the caudel fin within the first
20 seconds of exposure to air (Cooper et al. 2011), a
change that would diminish, not enhance, blood
flow. The fact that these changes were reversed
upon application of the -adrenoreceptor blocker
phentolamine indicates that this initial vasoconstriction was probably a catecholamine-induced response
to stress. Long-term acclimation to a terrestrial environment (10 days) induced cutaneous angiogenesis
(Cooper et al. 2011). Using immunohistochemistry
and the antibody for the endothelial protein
CD31 (Baluk and McDonald 2008), we showed an
increased CD31 signal in the caudal vessels of
air-exposed K. marmoratus (Cooper et al. 2011).
These results indicate that the turnover of endothelial cells or the overall number of endothelial cells
was increased in air. The fins of K. marmoratus constitute 40% of the body’s surface area (Cooper
et al. 2011), and therefore if angiogenesis is restricted
to the fins only (but may also be occurring across the
total surface of the body), then these changes would
potentially have a significant impact on the exchange
of gas during prolonged terrestrial episodes.
The skin of K. marmoratus appears to play a role
in sensing oxygen levels in the environment. In most
fish, hypoxia is detected by chemoreceptive neuroepithelial cells (NECs) in the gills (Dunel-Erb et al.
1982; Jonz and Nurse 2003; Saltys et al. 2006). Gill
NECs are positioned externally (where they are in
contact with the incident flow of water and may
detect aquatic hypoxia) or internally (where they respond to changes in oxygen levels of the blood)
(Perry et al. 2009). In some air-breathing fish, gill
NECs mediate hypoxia-induced air-breathing at the
surface (Smatresk 1986; Shingles et al. 2005; Lopes
et al. 2010). In K. marmoratus, NECs were found
in the gill and over the entire cutaneous surface,
occupying the uppermost epithelial layer (Regan
et al. 2011). NECs of both the skin and gills increase
797
Environmental physiology of the mangrove rivulus
cell area in response to chronic hypoxia, and pharmacological studies suggest that they may be involved in regulating the response to emersion in
K. marmoratus (Regan et al. 2011). Further studies
are required to determine whether cutaneous sensing
of oxygen is ubiquitous in air-breathing fishes.
Ionoregulation and osmoregulation
As mangrove rivulus move from water onto land,
they must maintain homeostasis of water and ions
without the use of branchial epithelium and possibly,
under some circumstances, in an environment with
5100% humidity. Variations in salinity commonly
occur in mangroves, both spatially (freshwater or
brackish streams flowing over mudflats) and temporally (heavy rainfalls versus dry season) (Gordon
et al. 1985). Even when fish leave water, the salinity
of the moist substratum would presumably vary depending on these same factors. Given these challenges, K. marmoratus managed to maintain perfect
whole-body homeostasis of Cl and water but not
Naþ balance over a 9-day period of exposure to air
in the laboratory (LeBlanc et al. 2010).
Ion-transporting cells (ionocytes) in the skin have
been reported in some amphibious fish but not
in others (Schwerdtfeger and Bereiter-Hahn 1978;
King et al. 1989; Yokoya and Tamura 1992). In
K. marmoratus, a rich population of ionocytes are
present on the cutaneous surface (Fig. 4A) as well
as on the gills (Fig. 4B). Skin ionocytes form clusters
of 20–30 cells and the physiological significance of
this pattern is unknown. Is the clustering synchronous with the discontinuous subepidermal scales
and/or with the coordinated signaling pathway
Delta/Jagged-Notch that regulates cell clustering in
zebrafish embryos? (Hsiao et al. 2007; Jänicke et al.
2007) Further studies are required to understand the
functional role of these clusters in K. marmoratus.
Cutaneous ionocytes are probably the key site of
ion transport when K. marmoratus are emersed. The
surface area of cutaneous ionocytes was larger in
air-exposed rivulus in contact with a moist hypersaline (45ø) compared with a freshwater (1ø)
surface, suggesting that a larger surface area of
cells would be beneficial for ionoregulation at
the higher salinity (LeBlanc et al. 2010). The
number of mucous cells declined significantly
in air-exposed rivulus (45ø substrate), indicating
that increased mucus production in K. marmoratus
is probably not a strategy that protects body tissues from dehydration in air, unlike the case for
other air-breathing fish (Lam et al. 2006). Do
other structural changes occur in the skin that
Fig. 4 Representative fluorescent images of 2(4-dimethyl-aminostyryl)-1-ethyl-pyridinium (DASPEI)-stained
mitochondrial-rich cells (ionocytes) in the skin (A) of
K. marmoratus acclimated to seawater (45ø). The cells form a
clustering pattern with 20–30 cells/cluster. Scale bar ¼ 100 mm.
(B) The antibody to NaþKþATPase was used to identify
ionocytes in the gills of K. marmoratus exposed to air for 9 days
over a moist (45ø) surface. The image shows a single filament
with no evidence of individual lamellae. The ionocytes are
mostly embedded within the mass of cells on the filament and
the interlamellar space. Scale bar ¼ 50 mm. From LeBlanc
et al. (2010).
retain body water but exchange critical molecules
during prolonged exposure to air? There are many
avenues for further investigation.
Volatilization of NH3
Animals catabolize proteins and amino acids for fuel
and maintenance/turnover of body proteins, resulting in the synthesis of ammonia (Wright 1995).
Ammonia is a neurotoxin and elevated concentrations of ammonia in the tissues are harmful to fish
(reviewed by Ip et al. 2001). Ammonia exists in
solution as both the dissolved gas NH3 and the ion
NH4þ, although at physiological pH the equilibrium
is shifted toward NH4þ (pKamm 9). Normally, fish
excrete ammonia as NH3 down the gill’s
blood-to-water NH3 partial pressure gradient by
798
way of ammonia gas channels, the Rhesus (Rh) glycoproteins (for reviews see Weihrauch et al. 2009;
Wright and Wood 2009). Diffusion of ammonia
across the gills and its dilution in the aquatic environment prevents its accumulation in the tissues, but
elevated environmental levels or exposure to air may
prevent efficient elimination of waste nitrogen.
When K. marmoratus are out of water, accumulation of ammonia is avoided by its excretion through
alternative routes (see below) or its conversion to
less toxic compounds (e.g. urea, glutamine). Urea
is a byproduct of arginine catabolism, uric acid degradation, or, in a few unusual cases in fish, the end
product of the ornithine urea cycle (OUC)
(Anderson 2001). The percent of nitrogen excreted
as urea in tropical amphibious fishes varies between
3 and 58% (Graham 1997), with mangrove rivulus
excreting 10–40% as urea (Frick and Wright 2002a;
Rodela and Wright, 2006a,b). K. marmoratus do not
appear to synthesize urea via the OUC because activities of OUC enzymes were relatively low and only
modestly increased in response to exposure to air
(Frick and Wright 2002b). Thus, urea production
in K. marmoratus is likely the result of a combination of arginolysis and uricolysis.
Our work shows that in air, K. marmoratus are
one of the rare teleosts that volatilize a significant
amount of NH3 from the cutaneous surface (Tsui
et al. 2002; Frick and Wright 2002b; Litwiller et al.
2006). An 18-fold increase in NH4þ concentration
and a small elevation of pH at the skin’s surface
result in a substantial rise in cutaneous partial pressure of NH3 (Litwiller et al. 2006). These changes in
the ion composition of the surface of the skin may
be related partly to changes in the rate of transport
of NH4þ/NH3 and Hþ (C. Cooper et al., submitted
for publication). An induction of Rh glycoproteins
Rhcg1 and Rhcg2 mRNA in air may translate into an
increase in apical Rhcg proteins in cutaneous ionocytes (Hung et al. 2007; Wright and Wood 2009),
facilitating transfer of NH3 to the skin’s surface.
Overall, K. marmoratus are highly efficient in eliminating ammonia when emersed because over a
10-day period there was no significant accumulation
of whole-body ammonia (Frick and Wright 2002b).
P. A. Wright
K. marmoratus shares responsibility for gaseous exchange (Ong et al. 2007; Regan et al. 2011), ionoregulation (LeBlanc et al. 2010), and excretion of
nitrogenous wastes (Frick and Wright 2002a;
Litwiller et al. 2006; Hung et al. 2007; Wright and
Wood 2009) with the gills when immersed but plays
a more dominant role when fish emerse. Angiogenesis in the fins could potentially increase blood flow
and enhance the capacity for cutaneous exchange in
air (Cooper et al. 2011). Moreover, there is a strong
potential for further insights into regulatory pathways by identifying differences among strains in
responses to environmental perturbations using isogenic lineages of laboratory-reared K. marmoratus.
Acknowledgments
I thank my students N. Frick, S. Litwiller, K. Ong, D.
LeBlanc, K. Regan, and A. Turko and collaborators
Drs. C. Wood, M. O’Donnell, C. Murrant, J. Wilson,
D. Fudge, C. Hung, C. Cooper, E.D. Stevens, S.
Consuegra, and S. Currie for their contributions to
this research. A special thanks to Dr. D. Noakes for
introducing me to K. marmoratus in the laboratory
and Dr. D.S. Taylor for sharing his passion for the
mangroves. I also thank I. Smith, B. Frank, M.
Cornish, and Lori Ferguson who provided technical
assistance at the University of Guelph. The Calabash
Caye field trip in December 2009 included Drs. C.
Cooper, S. Consuegra, S. Currie, D.S. Taylor, P.
Wright, and graduate students A. Elinson and K.
Regan. I am grateful to E. Orlando, B. Ring, and
D. Bechler for organizing the Mangrove Killifish
symposium.
Funding
Supported by National Institutes of Health grant
R15HD070622 from the Eunice Kennedy Shriver
National Institute of Child Health and Human
Development;
Society
for
Integrative
and
Comparative Biology through the DCE, DCPB,
DAB, and the C. Ladd Prosser Fund; and the
College of Agriculture and Natural Resources,
University of Maryland. The NSERC (Canada)
Discovery Grants Program has funded the research
on K. marmoratus in the Wright laboratory.
Perspectives and Conclusions
Supplementary Data
Mangrove rivulus are extremophilic fish that breathe
cutaneously when emersed. They are an ideal model
species for examining the specific mechanisms of cutaneous exchange that air-breathing fish use to maintain homeostasis over long periods of exposure to
air. Our studies have demonstrated that the skin of
Supplementary Data are available at ICB online.
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