sexton beetles behavioural adaption to maximize utilization of valuable and unpredictable resource and increase reproductive opportunity.

2. “Tale of Sexton Beetles”
Behaviour and Ecology
Ravi Biradar
PHD16AGR6008

3. Index
• Introduction
• Composition of sexton communities
• Resource Partitioning
• Competition with other taxa
• Symbiosis with phoretic mites
• Larval begging and filial cannibalism
• Biparental care
• Alternative male-mate finding tactics
• Communal breeding
• Mimicry
• Conclusion

4. Introduction
• Extended biparental care of young and of reproductive cooperation between
and within the sexes. Yet within cooperative associations there is often
conflict.
• Frequently the interests of cooperating individuals differ as each seeks to
maximize its own fitness.
• Changing the effectiveness of cooperation, which shifts the balance between
cooperation and conflict.
• The costs and benefits of cooperation are shaped by the environment.
• Resource: Small vertebrate carcasses: Birds and rodents

5. Who I Am…. ?
Sexton beetle: Nature’s undertaker
 Carrion beetle
 Grave digger: Burying Beetle
 Nutrient recycler
 Post mortem interval
 Endangered Species: 1989

6. Where I stand… ?
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Silphidae (15 genera and 183 species)
Subfamily: Silphinae (12 genera and 111 species)
Subfamily: Nicrophorinae (3 genera and 72 species)
Genus: Nicrophorus (68 species)
 Silphids are the Carrion Beetle but not all silphids are sexton beetles

7. (Sikes and venables 2013)

8. • Small vertebrate carcasses: Birds and rodents
• This resource is necessary for reproduction, is unpredictable in space
and time, and is valuable to many other taxa.
• Consequently, burying beetles treat each reproductive event as if it
were their only opportunity to breed
• They behave to maximize their lifetime fitness with their current brood
alone.
Why do they bury carcass….??

9. Burying beetle parents feed their young….. so what do they do exactly?
 They can bury corpses that weigh up to 500 times as much as themselves
Beetles discover a carcass with their sensitive chemosensors : 2 miles away
 Once buried, the carcass is rolled into a ball, stripped of its fur or feathers
 The female lays eggs in the soil nearby.
(Royle et al., 2012)

10.  Brood chamber, known as the ‘crypt’
 Embalm the carcass using anal and oral anti-microbial secretions to slow
putrefaction.
 The altracial larvae hatch crawling to a bowl-shaped crater on the
prepared carcass
 They meet their parents, started begging and enjoy their first meal (a
soup of partially digested carrion)
(Royle et al., 2012)

11. Life Cycle…
• Depending on the temperature, size of carcass and species of beetle
(Royle et al., 2012)

12. Diversity and Distribution
• Nicrophorus is a northern hemisphere genus of about 68 species.
• Both population densities and species diversity are higher in northern
localities
• Amphipolar and amphitropical
• lack of success in southern locales include increased competition with
ants, flies and perhaps vertebrates, as well as increased rates of carcass
decomposition.
• Southern scale: Latin America or Southeast Asia
(Bartlett, 1988)

13. (Encyclopedia entomology, 2018)
Locate me in map….

14. Necrophila cyaniventris
Nicrophorus nepalensis Necrophila ioptera Necrophila (Deutosilpha) rufithorax
Necrodes littoralis Necrodes nigricornis Thanatophilus minutus
Indian Sexton’s
(Bala and Singh, 2017)

15. Resource Partitioning
• The “small carrion” niche is somewhat differentiated by spatial and
temporal patterns of activity and somewhat by body size of beetles,
which dictates preference in carcass size.
• In each location there is a guild of four to six species of burying
beetles that has a similar pattern of seasonal and temporal activity
and habitat use.
• In each exists a very large species (Nicrophorus germanicus and
Nicrophorus americanus )
(Wilson, 1984)

16. SEASONAL AND TEMPORAL PATTERNS:
• Emergence times and patterns of sexual maturity differ, causing
some species to be univoltine and multivoltine.
• Competition between the two species appears to be temperature
dependent
• Different patterns of daily activity and flight periods
• N. defodiens geographical range is probably determined by
competition with N. orbicollis. N. orbicollis is larger and can displace
N. defodiens on a carcass.
• N. orbicollis finds the highest proportion of experimental carcasses
on relatively warm nights, but N. defodiens can find and bury
carcasses at lower temperatures.
(Wilson et al., 1990)

17. Habitat preference:
• Perhaps the most important habitat characteristic is the soil
composition and texture.
• Smaller species find it easier to dig in damp soil that is rich in organic
material and typical of coniferous forests
• larger species can manage in the dry, somewhat sandy soil of the
hardwoods.
• Seasonal occurrence, habitat preferences and local abundance the
probability of encountering a conspecific versus a congeneric varies by
species, time and habitat.
• Major sexton beetle competitor that an individual faces may always be
a conspecific, may shift seasonally or for uncommon species, may
usually be a congeneric.
(Pukowski, 1933)

18. Ecological characteristics of major species of sexton beetles
(Nicrophorus) communities of northern hemisphere
* Diurnal species ** Crepuscular species others are nocturnal species
(Scott, 1998)

19. CARCASS SIZE:
• Bury any type of small vertebrate carcass ( no difference in birds &
mammals
• Although N. orbicollis is about four times heavier than N. defodiens,
the former will bury and can rear a brood on carcasses as small as 7
g, whereas the latter will bury and rear a brood on 4-g carcasses.
• In northern Michigan, over 90% of very small carcasses (4–6 g) are
buried by N. defodiens, even though N. orbicollis is abundant.
Intermediate size carcasses (21–90 g) are often buried by N.
defodiens
• Very large carcasses (120–210 g) by N. orbicollis.
(Trumbo, 1992)

20. Competition with other taxa
• The importance of competitors other than beetles varies with
latitude, habitat and season.
• Vertebrates: skunks and racoons more in southern USA than
northern part of the state.
• N. orbicollis is the top competitor in the northern locale
• Microorganisms are more serious competitors on relatively large
carcasses than on smaller ones.
• Flies: competition is high in summer.

21. Symbiosis with phoretic mites
So we can call “carry-on beetles”… !
• Sexton beetle: pays a huge cost carrying the mites: heavy and affect its ability
to move and fly
• Mite: eat the maggots, the fly eggs and larva of anything that is not a carrion
beetle.
Attack force on congeric competitiors
Poecilochrus ( Mesostigmata, parasitidae)
•P. Carabi – N. vespillodies
•P. necrophori--- N. vespillo
(Nehring et al., 2017)

22. Larval begging and filial cannibalism
• Begging is a form of sibling competition
• Larval to be begging: raising its head-waving its legs/ touching the
parent- mouth to mouth contact.
• Control over resource allocation
• Incure fitness cost: larval growth and development
• Is begging costly ..?

23. Live dead Live dead
o Junior • Senior

24. Findings
1) Seniors were more successful in gaining access to the parent’s
mouthparts than juniors
2) Begging increased the probability that a larva fell victim to
cannibalism during brood reduction.
3) The risk that a begging larva fell victim to cannibalism was more
than 13 times greater than expected if parents targeted larvae
irrespective of their behavior.

25. Parental care

26. Sex roles in parental care
(Kokko and Jennions, 2008)

27. (Suzuki, 2012)

28. Biparental care
• Bonanza resource: carrion
• it is valuable and unpredictable and must be defended from a
diverse group of organisms that would also exploit it.
• Thus, burying beetles conceal a carcass underground and continue
to guard it to prevent its use by vertebrates, other insects and
microbes.
• major factors promoting post-ovipositional investment. These
factors include:
• (a) The potential gain from each parent’s ability to increase
offspring survival and competitive ability
• (b) The potential loss from reduced future fitness
 if additional reproductive opportunities are lost while providing
care
 if providing care reduces future fecundity. (Zeh and smith, 1985)

29. Parental behaviour and its effects
Parental behaviors:
• Both spend a large proportion of their time in carrion and brood
chamber maintenance, provisioning of offsprings
• Both regulate the brood size on small carcasses by committing
infanticide on superfluous young.
• Female spend significantly more time feeding larvae than do males.
• Single males compensate for mate loss by increasing their feeding
rates to match those of single females.
• The survival or final weight of larvae does not differ if they are
reared by single male or single female parents
(Fetherston, 1990)

30. Behavioral observation
Provisioning larvae:
Processing carrion:
Carcass maintenance:

32. Findings…..
 Females did not significantly change the time spent on any of the
three parental behaviours in response to the removal of the male.
 In contrast, males responded to the removal of the female by a
significant increase in the time spent provisioning larvae and
processing carrion.
 The removal of the female had no significant effect on the time
spent on carcass maintenance by males.
 Thus, only male parents adjusted the amount of time spent
providing care in response to the removal of their mate.

33. FEEDING:
• larger species that require parental feeding and not necessary in small
species
• N. invistigator & N. humator
• N. orbicollis, & N. sayi
• N. defodiens, N. tomentosus & N. vespilloides: survives without parental
feeding
• Feeding is not the primary selective force for the evolution of parental care
in Nicrophorus, but rather feeding is the price paid for rapid larval growth
to a larger size.
• The number of larvae reared and the total mass of the brood is positively
correlated with carcass mass and not with the number of parents present,
their size, or how long they provide care.
• Absence of competition, the quantity or quality of parental care is not the
principal determinant of reproductive success; the size of the carcass is.

34. DEFENSE AGAINST COMPETITORS AND PREDATORS:
• Two beetles were long assumed to be able to conceal the carcass faster than
one, even though their interactions are not at all coordinated.
• Females of small beetle species, N. vespillo and N. vespilloides, lose their lives
only to large staphylinid predators. replacement clutches after brood failure.
• Conspecifics competition: large members replace same-sex residents on a
carcass
• Male assistance:
– may help keep fungi in check.
– greatly reduces the probability of an intraspecific take over.
– Make the carcass less vulnerable to detecting of carcass.
(Scott, 1990)

36. (Shippi et al., 2018)

37. Findings….
• Female residents being more successful in defending their brood and
engaging in more fights than male residents. Because they put more effort
into brood defence.
• No difference between female and male intruders in their success at
taking over the carcass from resident.
• More fights between residents and intruders when the intruder was male
rather than female. Because male intruders put more effort into taking
over carcasses from the resident than female intruders.

38. Duration of paternal care
• The effectiveness of this protection also varies with the type of
competitor.
• The duration of male care is quite variable both among species and
among populations and it is related to:
– The vulnerability of the brood
– Stage of larval development
– Carcass depletion
• If the female parent dies, deserts, or is removed experimentally, the
benefit of male care is increased.
• Males that are single parents remain with the brood significantly
longer

39. (Scott, 1998)

40. Conflicts of interests between males and
females
• In species with high parental investment by both males and
females, there is usually much less conflict in their interests than in
species with high female-only investment.
• Males may be forcibly evicted, especially from very small carcasses.
• Female N. vespillo forcing males to leave soon after burial. When
breeding on very small carcasses (5 g) in the laboratory, males may
even be killed by females.
(Pukowski, 1933)

41. Alternative male mate-finding tactics
• A distinctive posture and releases a pheromone to attract a female.
N. vespilloides
N. humator even when they do not have a carcass.
N. defodiens
• Although these females mate with additional males, a non–carcass
holding male can expect 5–10% paternity of the female’s next
brood.
• N. vespilloides, which uses this tactic, has a high rate of broods
reared by single females (39%), whereas N. orbicollis, which does
not advertise without a carcass, has a lower rate (11% to 22%).
(Eggert, 1992)

42. Communal breeding
• Extensive biparental care, have social behavior that extends beyond such
cooperation.
• Both males and females of some, perhaps most, species often bury a carcass
and rear a single brood with others of their sex.
• These groups can be quite variable in composition; groups of N. tomentosus
consist of 0–6 males and 1–7 females.
• Subsocial behaviour Quasisocial behaviour
(Trumbo and wilson, 1993)

43. Frequency of communal breeding
• N. orbicollis: rare communal breeding (except large carcass)
• N. defodiens, N. tomentosus, and N. vespilloides: are all often
found in cooperative associations
• There is a trend for females to enter into communal breeding
more readily than males.
(Trumbo and wilson, 1993)

44. Carcass size:
• Multiple males and/or females of both N. orbicollis and N. defodiens are
twice as commonly found on 50- to 90-g carcasses as on 20- to 30-g ones.
• 50% of 40 to 45 g carcasses but 75% of 55 to 60 g carcasses were buried
and prepared by more than one male and/or female N. tomentosus.
• Communal breeding is more common on relatively large carcasses
• Two females can rear more larvae than one on relatively large carcasses
but not on smaller ones.
(Trumbo, 1992)

45. Mimicry… ?
Necrophorus tomentosus (Heinrich, 2012)
B. ternarius
B. rufocinctus
B. vagans
B. bimaculatus
B. sandersoni
B. impateins

46. (Heinrich, 2012)
Over all is an apparent combination of both Mullerian and Batesian mimicry of bumble bees

47. Conclusion
• These beetles must coordinate reproduction with the location of a
necessary resource that is unpredictable in time and space, an
reproduction must be coordinated with a mate.
• Their behavior must undergo regular changes from competitive to
cooperative and parental.
• Hormonal mechanisms are expected to play a major role in
orchestrating the interplay between behavior, the social and non-
social environment.