Biology of Sharks and Their Relatives Flashcards
When was the origin of chondrichthyans?
400 million years ago
What are the synapomorphic (ancestral) characteristics of chondrichthyans?
- cartilaginous skeleton
- claspers for internal fertilization
How many described species of elasmobranchs? Sharks?
Approximately 1200 species of elasmobranchs. Approximately 500 species of sharks.
anguiliform locomotion
entire trunk (body) and tail participate -orectolobiformes, scyliorhinids
carangiform locomotion
posterior half of body participates
-squaliforms, carcharhiniforms, some lamniforms
thunniform locomotion
only tail and caudal peduncle participate
-most lamniforms
undulatory locomotion
pectoral fins anterior to posterior order participate
-most batoids (benthic rays and skates)
oscillatory locomotion
flapping pectoral fins
-pelagic rays (mantas, eagle rays)
What is the body shape of lamnid sharks?
To increase streamlining and reduce drag…
- large pectoral fins
- narrow caudal peduncle with keels
- symmetrical caudal fin
- reduced pelvic, 2nd dorsal, and anal fins
How do sharks maintain a vertical position in the water column with negative buoyancy and water flow?
Tilt the body slightly upward. The slower the swimming, the greater the tilt needs to be to remain in vertical position in the water column
What is the function of the caudal fin for swimming?
thrust and lift by moving water posteriorly and ventrally in vortex rings
What is the function of the pectoral fins?
The angle of the fins are adjusted for vertical movements
ceratotrichia
cartilaginous rays in the fins (used for shark fin soup)
apleisodic fins
less stiff, more maneuverable (common in benthic species)
pleisodic fins
more stiff, reduced drag (lamniforms)
Describe the elasmobranch feeding apparatus
- composed of 10 cartilaginous elements (simple!)
- no pharyngeal jaws
- still allows for great diversity of feeding mechanisms and behaviors
What are the types of feeding mechanisms used by elasmobranchs?
- ram feeding
- suction feeding
- ram filter feeding
- biting
ram feeding
swims over prey and engulfs whole or seizes it in its jaws
suction feeding
decrease in the pressure of the buccopharyngeal chamber to pull prey into mouth
ram filter feeding
continuously swims forward with mouth open
biting
takes of pieces of prey
What was the ancestral jaw like?
autodiastylic (jaw fused to upper cranium). Jaw suspension and protrusion evolved later.
What was the ancestral jaw like?
autostylic (jaw fused to upper cranium). Jaw suspension and protrusion evolved later.
Hyostylic jaws
The jaws are not directly connected to the cranium except by the hyomandibula (most sharks)
Euhyostylic jaws
Least connection of jaw to the cranium. Jaws can completely protrude (batoids)
How does body size relate to bite force?
Bite force increases with body size. This allows increase consumption of larger, more difficult prey
What is the approximate replacement rate of teeth?
Days to weeks. Depends on species, temperature, season, diet
heterodonty
change in size/shape of teeth in different parts of the jaw
ontogenetic heterodonty
changes in teeth shape/size related to body size/age.
-lamnid embryos have different teether than adults due to different diet (ova) and to not damage the uterus
How does metabolic rate change with size?
Mass-specific metabolic rate decreases with increased size
How does metabolic rate change with temperature?
Metabolic rate increases with temperature
How does lifestyle relate to metabolic rate?
Obligate ram ventilators have higher MRs than less active species
-continuous swimming pelagic predators (lamniforms) have highest SMR, MMR, and aerobic scope
How does endothermy relate to aerobic capacity?
Aerobic swimming is powered by red muscle. Regional endothermy warms red muscle, allowing increased aerobic capacity (higher enzyme activity to make ATP)
- requires increased supply of oxygen and aerobic fuels to the red muscle
- lamnids have higher oxygen uptake at the gills and delivery to red muscle
How does white muscle relate to anaerobic metabolism?
anaerobic metabolism is powered by white muscle and used during burst swimming
-lamnids also have high anaerobic capacity (possibly due to cardiorespiratory systems ability to deliver oxygen and metabolic substrates quickly)
Why use behavioral thermoregulation?
To get some potential energetic benefit (growth, digestion and assimilation, reproduction)
Why hunt warm rest cool?
Hunting warm increases MR and thus foraging efficiency. Rest (digesting) cool decreases metabolic rate, slows digestion, and increased digestive/assimilation efficiency.
How does endothermy relate to food digestion?
Increases rate of digestion
How does regional endothermy benefit reproduction?
Rete may keep repro system warm, speeding development. Particularly porbeagle and salmon shark that have additional kidney rete.
regional endothermy
ability to maintain core and other regions of the body at warmer temperatures than ambient
-aerobic swimming muscles, eyes, brain, viscera (organs)
How do lamniforms do regional endothermy?
Retain metabolic heat generated by continuous activity of aerobic (red) muscles during sustained locomotion, digestion, and assimilation
Where is red muscle loctated in ectotherms? endotherms?
Red muscle is near skin in ectotherms and near core in endotherms
Explain anatomy of regional endothermy
- dorsal aorta branches into lateral arteries that run length of body under skin. Lateral veins run in opposite direction
- branch arteries/veins (RETE) connect lateral artery/vein to red muscle
rete
branches of arteries and veins that connect red muscle to main lateral arteries/veins. The counter-current heat exchange allows red muscle near core, eyes/brain warmer than ambient
List the smallest to largest rete system of lamniforms
- common thresher
- longfin mako
- shortfin mako
- white shark
- porbeagle
- salmon shark
thermal excess
tissue temperature minus SST
What thermal excess is considered endothermy?
At least 2.7 celcius
What is physiological thermoregulation?
Regulating rates of heat retention and heat loss. This is likely done by altering blood flow rate and retial heat-transfer efficiency
How does regional endothermy benefit movement behavior?
Can stay in colder waters for longer and can make more frequent dives to colder water
How does regional endothermy related to blood-oxygen efficiency?
Warming blood decreases blood-oxygen affinity, therefore oxygen does not want to be delivered to red muscle easily. Lamnids have elevated HCT, Hb, and myoglobin that may buffer against this and ensure sufficient oxygen delivery to red muscle and other tissues.
Least biased way to describe diet?
Index of relative importance. Incorporates, frequency of occurrence in the species, count of prey, weight of prey
Why are there ontogenetic shifts in diet?
Changes in habitats and movement patterns, swimming speed, size of jaws, teeth, and stomach, energy requirements, experience with prey, vulnerability to predation
What is the evidence to suggest that most sharks are intermittent feeders (rather than continuous)?
High occurrence of individuals with empty stomachs and/or stomachs with small amount of prey in advanced stages of digestion
What is the trophic level of sharks as a group?
Tertiary consumers, trophic level >4
daily ration
mean amount of food consumed on a daily basis by individuals in a population (% body weight per day). Usually <3% in sharks
gastric evacuation
amount of time it takes food to pass through stomach
- generally takes 1+ days in elasmobranchs
- can vary with temperature, meal size, food type
spiral valve
intestine with high surface area for digestion and absorption but takes up less space (to allow for large liver and embryos). Also has slower digestion. Low rates of food consumption and digestion contribute to slow growth and reproductive rates
gross conversion efficiency
proportion of ingested food that will be available to the next trophic level (conversion of energy to growth)
testes
male gonad used for spermatogenesis and secretion of steroid hormones
-lamnids have radial testes where follicle development occurs in multiple lobes
ductus efferens
transports sperm from testes to epididymis
epididymis
complex tube that may function in protein secretion and sperm passes through to get to ductus deferens
ductus deferens
final sperm products are formed into clumps here and pass into seminal vesicle
-lamniforms have spermatophores (encapsulated clumps of sperm)
spermatophores
encapsulated clumps of sperm found in lamniforms
seminal vesicle
forms clumps of sperm, stores sperm
Leydig gland
secrete seminal fluids into epididymis and ductus deferens
alkaline gland
involved in sperm protection
claspers
copulatory organs
siphon sacs
flush water and sperm into female
ovary
generates germ cells, accumulates yolk, synthesizes/secretes hormones
-lamniforms have 1 ovary encapsulated in epigonal organ (immune function)
ostium
uses cilia to move fully developed eggs into anterior oviduct
oviducal gland (shell gland)
egg encapsulation, sperm storage, fertilization
-no sperm storage in lamniforms
isthmus
connects oviducal gland to uterus
uterus
embryo development or egg modification
leceithotrophy
embryos get nutrition entirely from yolk reserves within the egg case
matrotrophy
energy reserves present in the egg are supplemented by additional maternally derived nutrients obtained during gestation
What is the likely ancestral reproductive mode? What is the evidence?
Yolk sac viviparity
- Urea retention in ancestral species…likely used to detoxify ammonia produced in uterus
- evidence of intrauterine canabalism in ancestral secies
oviparity
eggs laid on seafloor, some development occurs outside the mothers body
single oviparity
eggs released one at a time (or pair) as they develop
retained oviparity
eggs retained in reproductive tract for some period of development
yolk sac viviparity
yolk sac is principal source of nutrition until parturition (much thinner egg envelope than oviparous species)
candle
egg envelope containing several fertilized eggs in some yolk sac viviparous species
mucoid histotrophy
additional nutrients from mucous produced by the uterous. Most viviparous species do this to a degree
lipid histotrophy
secrete a protein- and lipid-rich histotroph from secretory structures within the uterine lining (trophonemata)
trophonemata
secretory structures within the uterine lining that secrete histotroph in stingrays
placental viviparity
embryos develop a yolk sac placenta after the yolk within the external yolk sac is exhausted
- start with yolk sac, then mucoid histotrophy, then placenta
- yolk sac attaches to uterine wall and yolk stalk elongates to form placenta
- uterine compartments
- placentation occurs about 2-4 months after fertilization
- not a blood connection
appendiculae
flaps on the stalk/placenta that increase surface area and absorption of uterine secretion
carcharhiniform oophagy
unfertilized ova are contained within the same egg envelope as embryo and ingested
- one time contribution
- deepwater false catsharks
lamniform oophagy
continued production and delivery of ova throughout portion or most of gestation
adelphophagy
first embryo to hatch out of egg envelope within the uterus eats the other embryos and then ovulated ova
parthenogensis
female ability to reproduce without mating
-rare in captivity, young don’t survive long
reproductive cycle
time between ovulations
- vitellogenesis
- gestation
- resting (some species) where liver sequesters nutrients in prep for next vitellogenesis
embryonic diapause
delay in the development of young embryos within uterus
-my allow embryos to be born during time of year with optimal temperature or prey abundance
multiple paternity
females mate with more than one male
- increased genetic diversity, fitness, repro output
- multiple mating event could be a con for female
polyandry
female mates with multiple males
polygyny
male mates with multiple females
chyme
acidic, partially digested food that goes from stomach to duodenum
duodenum
beginning of intestine in sharks
pancreas
secretes pancreatic enzymes and bicarbonate rich juices to duodenum to raise pH of chyme and aid in digestion
gastrin
hormone that regulates secretion of digestive acids into stomach
secretin
hormone that stimulates the secretion of bicarbonate rich (basic) pancreatic juices into duodenum to raise pH
somatostatin
hormone that inhibits digestive processes and suppresses the production of gastric acids by inhibiting gastrin
gastrin-releasing peptide
hormone that promotes digestion by increasing blood flow to the gut
vasoactive intestinal polypeptide
hormone that promotes digestion by increasing blood flow to gut
peptide YY
hormone that suppresses digestion by reducing blood flow to gut and inhibiting gastric acid secretion and enzyme release
neuropeptide Y
hormone that suppresses digestion by reducing blood flow to gut and inhibiting gastric acid secretion and enzyme release
insulin
hormone that decreases glucose and increases glycogen storage after feeding
ghrelin
hormone that stimulates hunger
leptin
hormone that stimulates hunger
growth hormone
hormone that promotes somatic and skeletal growth
insulin-like growth factors
stimulate cell hypertrophy and extracellular matrix production
chromaffin tissue
neurosecretory cells along dorsal surface of kidney involved in stress response
- secretes catecholamines
- receives neural signals from stressors
catecholamines
- “fight or flight” stress amine hormones
- epinephrine and norepinephrine
- increase mobilization of energy reserves, increase ventilation and O2 uptake and delivery, increase BP to brain and muscles to promote transport of metabolic substrates, reduce blood flow to gut
hypothalamic-pituitary-interrenal axis
axis involved in sustained stress reponse, part of sympathetic nervous system
- corticotropin releasing factor (CRF) from hypothalamus
- adrenocorticotropic hormone (ACTH) from pituitary
- glucocorticoids from internal tissue
glucocorticoid function
sustained stress response
- increase glucose, increase metabolic rate, increase blood pressure, reduce inflammation
- suppress immunity, growth, reproduction over long term
What is the glucocorticoid in elasmobranchs?
1 alpha hydroxycorticoserone (1 alpha - OHB)
Why are there so few studies on the elasmobranch glucocorticoid?
There is no antibody specific to 1 alpha hydroxycorticosterone
-use corticoserone, the precursor to 1 alpha - OHB as proxy
How do sharks osmoregulate?
- regulate the concentration of urea, that is less toxic than ammonia but can help keep salts lower
- rectal gland secretes excess salts
What hormones are involved in elasmobranch osmoregulation?
- 1 alpha hydroxycorticoserone
- angiotensin II
- vasoactive intestinal polypeptide (VIP)
- C-type natriuretic peptide (CNP)
What is the role of 1 alpha-OHB in elasmobranch osmoregulation?
may play a role in rectal gland secretion
angiotensis II
hormone involved in sodium retention, influences electrolyte balance by reducing rates of glomular filtration and urine flow in kidney, inhibits salt release by rectal gland, increases drinking rate
vasoactive intestinal polypeptide (VIP)
hormone that stimulates salt secretion by rectal gland
C-type natriuretic peptide
hormone that stimulates VIP and salt secretion by rectal gland
Brain-Pituitary-Gonadal Axis
Primary endocrine system involved in regulating reproduction
Environmental signal initiate endocrine cascade
-gonadotropin releasing hormone (GnRH) from hypothalamus
-gonadotropins (GTHs) from pituitary gland (promotes gametogenesis)
-gonadal steroids from gonads
What are the roles of gonadotropin releasing hormones in elasmobranchs?
- travel in bloodstream to pituitary to stimulate the release of gonadotropins
- also have direct action on gonads to produce steroid hormones
Where are sex steroids produced in female elasmobranchs?
Ovaries
- granulosa and theca cells
- also corporea lutea for P4
What are the elasmobranch gonadotropins and what do they do?
- follicle-stimulating hormone
- luteinizing hormone
- promote gametogenesis and secretion of sex hormones in gonads
When does E2 peak during female reproductive cycle?
Follicular development
What are the roles of E2 during female reproduction?
- leads to synthesis of vitellogenin in the liver, which is transported to ovary and sequestered by oocytes
- assists in development/function of oviducal gland and may aid in egg encapsulation and sperm storage in the gland
- may play a role in placentation and secreting nutritive substances during pregnancy
- may be associated with sexual maturation
What are the roles of P4 during female reproduction?
- suppress E2 and vitellogenin production
- may be important for oviposition
When does P4 peak during female reproductive cycle?
during or shortly after ovulatory period
When does T peak during female reproductive cycle?
During follicular development with E2
What are the roles of T during female reproduction?
- serves as a precursor to E2
- may serve a role in sperm storage
Where are sex steroids produced in male elasmobranchs?
In the testes in the Sertoli cells (and supplemented in Leydig cells)
Where does spermatogenesis occur in elasmobranchs?
Leydig cells and Sertoli cells
What is the role of T and DHT in male reproduction?
- spermatogenesis
- copulatory behavior
- sexual maturation
What is the role of corticosteroids during reproduction?
-role in energy balance
relaxin
hormone that helps prepare for parturition
- increases cervix size
- maintenance of pregnancy prior to parturition
- high concentration in male semen that helps female uterine contractability to get sperm to egg
What is the role of thyroid hormones during reproduction?
-role in energy balance
calcitonin
hormone that may be involved in fetal nutrition and absorption of yolk sac
terminal nerve
connect brain to olfactory structures and a site of GnRH production
-GnRH produced here regulate reproductive processes and behaviors resulting from perception of olfactory cues linked with breeding (pheromones)
corpora lutea
temporary endocrine structure in ovaries involved in production of P4
-remains of the ovarian follicle that has released a mature ovum during a previous ovulation
Describe the size of the elasmobranch brain.
Relatively large brain
-comparable to birds and mammals in some sharks and rays
sensory sensitivity
minimum stimulus detectable
sensory acuity
ability to discriminate stimulus characteristics (direction, resolution, type/source)
Describe the elasmobranch eye
- small in relation to body size (eye size is larger in oceanic species, active species with active prey, and deep-dwelling species)
- nearly 360 degree vision
- nictitating membrane in charcharhinids and sphyrnids
- don’t change lens shape, move lens
- tapetum lucidum
- have rods and cons (debated weather they see color)
tapetum lucidum
specialized reflective layer behind retina that allows second chance for detecting photons and boost sensitivity in dim light
Describe the hearing anatomy and ability of elasmobranch.
- used for balance and sound perception
- sensory hair cells
- not as sensitive as teleosts
- sensitive to low frequency sounds
- can sense and response to pressure (depth, atmospheric pressure)
Describe mechanosenses in elasmobranch
- lateral line detects water movements (differential movement between the body and surrounding water)
- used for rheotaxis (orientation to water current), prey detection, predator avoidance, schooling, mating
- mechanosensory neuromast (group of sensory hairs covered by gelatinous cupula in pores)
- stimulated by sources up to 1-2 body lengths away
lateral line
cluster of pores along body filled with hair cells and gel that can sense water movements. Used for sense of mechanoreception
mechanosensory neuromast
group of sensory hairs covered by gelatinous cupula in pores along the lateral line. Involved in mechanoreception
Describe electrosenses in elasmobranchs.
- ampullae of Lorenzini
- electroreceptors sensitive to low-frequency electric stimuli
- orientation to local inanimate electrical fields, geomagnetic navigation, detection of bioelectric fields produced by prey, predators, and conspecifics
- pore with hair cells and hydrogel (creates voltage gradient)
Describe olfaction in elasmobranchs.
- inhalent and exhalent nostrils (nares)
- olfactory sac and rosettes (rosettes increase surface area)
- olfactory bulb (part of brain that that receives olfactory info)
- olfactory cues used to locate food
- turn towards nare that first receives odor cue
- approach odors from downstream
- excited by odors from stressed fish more than unstressed fish
- excited by amino acids and TMAO
- have receptors in mouth that closely resemble taste organs
How does the brain influence olfaction?
- threshold for olfactory-evoked feeding is lowered during starvation
- appears hypothalamus senses low blood dietary conditions and lowers threshold
What is the sequence of senses used at greater distances (sensitivity of senses from closest to farthest away)?
- electroreception (need to be closest)
- lateral line
- vision
- hearing
- olfaction (can sense from farthest distance)
