While most of the larvae out there are from crustaceans and insects, larvae come from a wide variety of taxonometric groups including several groups of Chordates. Today’s animal is one of my favorite larvae of all from Belize – the Spotted Trunkfish (Lactophrys bicaudalis (Linnaeus, 1758)). My idea of a perfect day out would be to dive on the reef at Carrie Bow Cay in the early morning and then spend the rest of the day snorkeling in the mangroves nearby, looking for and at the larval forms of fish and the invertebrates. So, on to the trunkfish…

Juvenile Spotted Trunkfish (Lactophrys bicaudalis)

While fish don’t go through complete metamorphosis, many species do go through radical changes from birth through “settlement”. In Belize many of the larval, and post larval juvenile, forms of reef fish can be found in the mangroves including the boxfishes (Ostraciidae), a family of teleost fish which includes fish often named cowfishes and trunkfishes. On my trip to Belize I was thrilled to find some juvenile spotted trunkfish, like the one above, among the mangroves myself. The above picture however is from the Smithsonian Institution’s Larval Fish Group. The Larval Fish Group is one of several excellent resources for larval fish.

Eventually this small (~1.0cm) larvae will grow to become an up to 40cm long (~16″) adult feeding on algae and small benthic (bottom) invertebrates such as mollusks, crustaceans, tunicates, sessile tunicates, and echinoderms (sea stars, sea cucumbers and urchins). They spawn at dusk releasing large eggs (~2mm) into the pelagic ocean. After hatching the larvae will remain in the nekton. The plates that form their armor begin to develop as lumps in the early preflexion larval stages. In Gulf of Mexico sampling they were rarely found and at the pre-settlement stages there were no uniquely distinguishing characteristics to allow identification of pelagic larvae to the genus or species levels. According to William’s wonderful Early Stages of Atlantic Fishes (Marine Biology), Ostraciidae spend a short amount of time as pelagic ichthyoplankton, settling rapidly to seagrass beds and mangroves. Eventually they do recruit back to the reefs to settle and develop a fiercely guarded territory on the reef.

Here then is the adult form:

mature Spotted Trunkfish

Two interesting bits about Spotted Trunkfish:

• They hunt by blowing jets of water into the sediments around the reef to uncover and dislodge the small inverts.
• Some boxfishes (Ostraciidae), including the Spotted Trunkfish (L. bicaudalis) have another form of defense beside their armor. They release a compound called ostracitoxin when stressed which can kill other fish, making members of the boxfish a poor choice for aquaria.

Classification

Kingdom

Animalia

Phylum

Chordata

Class

Actinopterygii (Ray-finned fishes)

Order

Tetraodontiformes (Puffers and filefish)

Family

Ostraciidae (Boxfishes, Cowfishes and Trunkfishes)

Genus

Lactophrys

Species

Lactophrys bicaudalis

References

Böhlke, J.E. and C.C.G. Chaplin, (1993) Fishes of the Bahamas and adjacent tropical waters. 2nd edition. University of Texas Press, Austin.

Richards, W.J.(ed.). (2006) Early Stages of Atlantic Fishes: An Identification Guide for the Western Central North Atlantic. Taylor and Francis, Boca Raton, FL pp. 2640.

Life Photo Meme

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Blowfly Larvae Photo by Leon Higley, UNL Entomology

Yummm… necrophagous larvae, or maggots, of the Blue Blow-Fly,Cynomyopsis cadaverina (Robineau-Desvoidy). The larvae of many species of fly feed on dead tissue. This is highly useful as an ecosystem service as they very effectively clean up any carrion that is missed or left over from any larger scavengers.

Some species maggots feed only on necrotic tissue leaving surrounding healthy tissue completely alone. These maggots clean out the dead tissue of large wounds in the wild and have been reintroduced to modern western medicine recently in a procedure called maggot debridement therapy. The therapy wass reintroduced by a Dr. R. Sherman from the Long Beach Veterans Hospital. He set up breeding of the Green Bottle Fly (Phaenicia sericata). These “Medical Maggots” are disinfected and introduced into wounds with non-healing necrotic tissues. The larvae dissolve and eat only the necrotic tissue, at the same time cleaning the wound of bacterial infection and the combined action of the necrotic tissue removal and secretions released in feeding significantly stimulate new healing of the wound.

C. cadaverina is also an important maggot, but it is used more in forensics. Different flies lay their eggs (oviposit) on carrion at different times and have different larval growth rates. By examining the maggots and eggs on a body and measuring the length and developmental stages of the maggots, forensic entomologists can determine roughly when death occurred. C. cadaverina oviposit 1.5 days after death according to Byrd & Castner’s Forensic Entomology. Of course th question can arise, how we know that a maggot arose from an egg laid on the body in question and whether it has actually fed upon the body. One way to find out ould be to examine the contents of the maggots gut. Of course the contents of the maggot’s gut aren’t like looking at the contents of a fish gut.

Jeffrey Wells and his colleagues needed just such a way of confirming that the maggots actually developed on the body for forensic investigations. They had three cases that come up in forensic investigations they wanted to be able to address:

• Investigators discover maggots but no body of any type, suspect possible foul play.
• Maggots are discovered, but not directly on a corpse, and alternative food sources are near.
• Maggots are found on a corpse, but may have come from somewhere else.

In the first case, if there are necrophagous maggots present there must have been a carcass nearby recently. If it was human then there may need to be an investigation. In the second case, because larva can crawl they may leave a corpse if disturbed or if the soft tissue is gone before they have grown enough to enter the pupal stage. If there are other food sources nearby the issue is to determine which food source the maggots originated on. Similarly in the third case it may be that the maggots found on a corpse may not have originated on that corpse as the maggots can crawl several meters and with the presence of other food sources may have crawled from a different source. If so those particular maggots should not be used to calculate the time of death.

Wells et al. raised eggs to the third instar maggots on human liver from a liver transplant patient. Since the eggs were collected from the wild, they allowed some maggots to pupate and were positively identified as C. cadaverina. They dissected the crops out of the maggots and adult flies and then extracted the DNA from the crops and their contents. The team performed two PCR reactions for each DNA extract. One PCR reaction used primers for fly cytochrome oxidase subunit one (COI), the other used primers for a region of human mtDNA. All the maggot and fly samples successfully amplified the fly COI fragment, and the human blood did not. The adult fly’s crops did not show human mtDNA as expected. They were able to successfully extract human mtDNA from the maggot crops that had fed on the donated liver as well as the blood sample donated by the liver transplant patient. The sequence from the maggot crops differed slightly (two position) from the blood sample. So they were able to conclusively identify maggots which had fed on human tissue, advancing the ability to use maggots in forensic investigations.

Classification

Kingdom

Animalia

Phylum

Arthropoda

SubPhylum

Hexapoda

Class

Insecta

Order

Diptera (Flies)

Family

Calliphoridae (Blow-flies)

Genus

Cynomyopsis

Species

Cynomyopsis cadaverina

References

J.H. Byrd and J.L. Castner, Editors, Forensic Entomology: The Utility of Arthropods in Legal Investigations, CRC Press, Boca Raton (2001)

J Wells, F Introna, G Di Vella, C Campobasso (2001). Human and Insect Mitochondrial DNA Analysis from Maggots Journal of Forensic Sciences, 46 (3)

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5th Instar, originally uploaded by eclectic echoes.

Now in the 5th instar, 53.9mm long on day 14 post hatch.

Many people are familiar with the incredible migration of the monarch butterflies from all over North America to Mexico. Coupled with it’s beautiful and distinctive coloration the migration is what makes this butterfly as well known and appreciated.

According to recent DNA analysis by Smith et al. in 2005, there are actually two sub species of Danaus plexippus. The nominate, migratory species we have featured here is Danaus plexippus plexippus and there is a non-migratory species found from Georgia west to Texas south through the Caribbean and Central America to the Amazon Basin named Danaus plexippus megalippe. South of the Amazon is separate species of monarch (D. erippus) that Smith et al. estimated split form the D. plexippus only 2mya.

The migratory subspecies essentially has two separate life cycles. The migrants overwinter in Mexico (where there are now significant anthropogenic pressures on their overwinter site) then in the spring mate and return to the southern part of the United States. They lay their eggs on the spring milkweeds in the south then die. The eggs that survive and make it to adults continue the migration northwards, each generation living as adults only for three to four weeks.

In late August and September cooler nights signal a change in the cycle. The last generation, now 3-5 generations removed from the spring’s migration group, do not complete reproductive development and will not become reproductively active until the following spring. This group has a significantly lower activity in a key hormone for development – “Juvenile Hormone” (JH). The JH deficiency stops development, and significantly extends the butterfly’s longevity, from a few weeks in summer butterflies to several months in the migrants. Experimenters have manipulated JH in non-migratory adult butterflies with the predicted changes in reproductive activity and longevity.

One of the most remarkable things about the migration of monarchs is that each year the migrants are on their maiden voyage. The entire migration route and cues are genetically wired. In their paper “Chasing Migration Genes: A Brain Expressed Sequence Tag Resource for Summer and Migratory Monarch Butterflies (Danaus plexippus)“, Haisun Zhu, Amy Casselman and Steven M. Reppert created a library of expressed sequence tags (EST’s) for D. plexippus plexippus. An expressed sequence tag is a unique sub-sequence of DNA in the encoding region of a gene which can be used to positively ID the gene and help map the gene to a specific chromosome location.

The researchers created the library with samples from both non-migrating (summer) and migrating (fall) butterflies. They estimate that their library could represent about 52% of the encoding potential of the D. plexippus genome. Throught the library they discovered that three genes (allatotropin, juvenile hormone acid methyltransfersase, and takeout) are responsible for increased JH activity in summer butterflies. The library also contained several genes identified with the circadian clock which governs and guides the monarch migration and a new allele of an Na+/K+ ATPase in summer only monarch which should confer more resistance to the toxic effects of milkweed than that reported previously.

Classification

Kingdom

Animalia

Phylum

Arthropoda

SubPhylum

Hexapoda

Class

Insecta

Order

Lepidoptera (Butterflies and Moths)

Family

Danaidae (Milkweed Butterflies

Genus

Danaus

Species

Danaus plexippus

References

Haisun Zhu, Amy Casselman, Steven M. Reppert, Dawn Albertson (2008). Chasing Migration Genes: A Brain Expressed Sequence Tag Resource for Summer and Migratory Monarch Butterflies (Danaus plexippus) PLoS ONE, 3 (1) DOI: 10.1371/journal.pone.0001345

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4th Instar, originally uploaded by eclectic echoes.

This is the 4th instar stage Danaus plexippus larva (monarch caterpillar). It is 11 days post hatch and 26.2mm long.

Very few eggs laid actually make it to become pupae, let alone successfully pupate into healthy adults. The sources of mortality are many and come at different stages of the life cycle. Monarch eggs and larvae are routinely eaten by several insects and arachnids, and parasitized by flies and wasps.

One predator of D. plexipus is the non-native Asian lady beetle, Harmonia axyridis, which was intentionally introduced to the United States as a biological control as far back as 1916. H. axyridis preys primarily on aphids as many other lady bird beetles, but it also eats other soft bodies insects such as larval stages of Lepidoptera. H. axyridis has become a dominant generalist predator in many agricultural areas of the United States where common milkweed and D. plexipus are common as well.

In a 2003 paper published in the journal Biological Control, R.L. Koch et al. quantified the predation of H. axyridis on D. plexippus in both laboratory and controlled field experiments. They found that the 3rd instar lady bug larvae preyed on monarch eggs at a rate of up to 25 eggs per larvae per day. The rate of predation on 1st instar D. plexippus larvae was as high as 15 per H. axyridis per day. The adult H. axyridis also preyed on the eggs of D. plexippus at a rate that is a linear response to the prey density.

Though the field and lab experiments were conclusive that H. axyridis will eat significant numbers of eggs and 1st instar larvae of D. plexippus, these trials were conducted without aphids present. The availability of aphids may reduce predation rates on both eggs and 1st instar monarch larvae.

In our own garden we have seen a single D. plexippus egg hatch outside with a 1st instar larvae that was not seen after the first day. We “rescued” one viable egg and raised it indoors as an experiment for our son. We counted 14 other eggs which were positively ID’d and examined under dissecting microscope. All were found to have been penetrated with a slit cut into the wall of the egg and the egg insides eaten, often with a trail left on the outside of the egg.

In obtaining food for the 4th and 5th instar stages of the monarch, we cut a common milkweed plant at its base and brought it home. Each leave was examined for eggs, mites and fungus then washed and stored in a ziplock with dry papertowel in the refrigerator. That single plant had a further 16 egg remains on it. Each of which had a narrow slit through the case.

Empty, originally uploaded by eclectic echoes.

Classification

Kingdom

Animalia

Phylum

Arthropoda

SubPhylum

Hexapoda

Class

Insecta

Order

Lepidoptera (Butterflies and Moths)

Family

Danaidae (Milkweed Butterflies

Genus

Danaus

Species

Danaus plexippus

References

R Koch (2003). Susceptibility of immature monarch butterfly, Danaus plexippus (Lepidoptera: Nymphalidae: Danainae), to predation by Harmonia axyridis (Coleoptera: Coccinellidae) Biological Control, 28 (2), 265-270 DOI: 10.1016/S1049-9644(03)00102-6

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Egg Mk. III, originally uploaded by eclectic echoes.

Egg Mk. I hatched outside, but the caterpillar disappeared when only 1-2 days old (presumed eaten)

Egg Mk. II I believe was the victim of a parasitic wasp or fly. Under the scope the yellow mass outside the empty, but non-eaten, egg looks to be the remains of a caterpillar that has exploded(?)

This egg is literally just a speck. This shot (a 1:1 pixel crop from the large size) was with a 100mm Macro, a 1.4x teleconverter and 48mm of extension tubes.

The egg itself is 0.5 mm (0.02″) in diameter and ~1.0 mm (0.04″) in height.

We watched the butterfly that laid an earlier egg (Egg Mk. I) on these same plants. She went from plant to plant sampling the nectar and exploring the leaves. She chose what appeared to be the healthiest of the four plants in the garden to lay her egg on. We judged it as the most healthy because when it was recently transplanted it had the largest most robust root system and it had recovered faster from the transplanting. When Egg Mk. I was laid all the plants, but one, were visually the same and appeared fully recovered from transplanting. The recent two eggs were similarly laid on the same plant. What made all three females choose the same plant?

Butterflies have complex chemoreceptors on their tarsi (roughly analogous to feet), which allow them to taste the flowers and leaves they land on. Several researchers have explored the chemical cues for oviposition (laying of eggs) in monarchs. They have found that certain flavinoid compounds in host plants play a role in stimulating oviposition in butterflies. When a female butterfly lands on a milkweed plant such as our butterfly weed (Asclepias tuberosa), using the tarsi on her forlegs and mid legs and using chemo receptors on the tips of her antennae, she can “taste” the species of plant, it’s age, physiological condition and key compound concentrations.

Monarch butterflies, like all Danaidae butterflies, lay their eggs on, and as larvae feed on, milkweed plants of the genus Asclepias. One characteristic of these plants is that they all contain cardenolide glycosides, a toxic steroid that can cause heart arrest in most vertebrate animals (notable exceptions include the black backed oriole which is a primary predator of monarch butterflies). Monarch larvae take up the cardenolides and sequester them in their body, so it is an important compound for the survival of the larvae and adults. In too high a concentration however, it can negatively impact larval development and even cause larval mortality, especially in the first instar stage. Too low a concentration and there is little or no actual chemical defense afforded to the butterfly, too high a concentration the butterfly risks increased mortality and deformity.

So our female butterfly was carefully selecting which plant to lay her egg on, to give the larvae the best chance of success.

Classification

Kingdom

Animalia

Phylum

Arthropoda

SubPhylum

Hexapoda

Class

Insecta

Order

Lepidoptera (Butterflies and Moths)

Family

Danaidae (Milkweed Butterflies

Genus

Danaus

Species

Danaus plexippus

References

Robert Baur, Meena Haribal, J. Alan A. Renwick, Erich Stadler (1998). Contact chemoreception related to host selection and oviposition behaviour in the monarch butterfly, Danaus plexippus Physiological Entomology, 23 (1), 7-19 DOI: 10.1046/j.1365-3032.1998.2310007.x

M. P. Zalucki, L. P. Brower, S. B. Malcolm (1990). Oviposition by Danaus plexippus in relation to cardenolide content of three Asclepias species in the southeastern U.S.A. Ecological Entomology, 15 (2), 231-240 DOI: 10.1111/j.1365-2311.1990.tb00804.x

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